Systems Operation

Usage:

Introduction

Power Train Electronic Control System Block Diagram

The Power Train Electronic Control System performs the shifting of the electric shift transmission. The electronic control module (ECM) responds to the shifting requests of the operator by activating the appropriate clutch solenoid valves which then allow oil to flow to the corresponding transmission clutches. In addition to the shifting function, the ECM also controls the neutral start function and the backup alarm function.

Also featured is a STIC controller and electronic torque converter. The ECM controls the impeller clutch and lockup clutch functions of the torque converter. These machines also have an additional feature called Reduced Rimpull. This allows the operator to select a preset amount of rimpull reduction desired.

Components Description

For the location of components, see the Parts Manual and the Electrical System Schematic in the machine Service Manual.

Electronic Control Module (ECM)

Electronic Control Module (ECM)
(1) Connector J1. (2) Connector J2.

The ECM makes decisions based on input and memory information, then the corresponding response is made through the outputs. The inputs and outputs of the ECM are joined to the machine harness by two 40 contact connectors.

Inputs

Numerous inputs inform the ECM of the status of the machine conditions. Two types of inputs exist; switch type and sensor type. Switches provide an open, grounded, or +battery signal to the switch inputs of the ECM. Sensors provide a constantly changing signal to the sensor inputs of the ECM. The inputs are listed on the Contact Description Chart.

Outputs

The ECM responds to decisions by sending electrical signals through the various outputs. The outputs either create an action or provide information. The outputs are listed on the Contact Description Chart.

Input/Output

The data link is used to communicate with other electronic control modules on the machine. The data link is bidirectional; which allows the power train ECM to receive and send information. The data link allows the sharing of information with other electronic control modules.

All electronic controls that use the data link are assigned a module identifier (MID). The MID for this power train ECM is the number 081.

Switches

Switches provide an open, ground or +battery signal to the switch type inputs of the ECM. Switches are two state devices; either open or closed.

* When a switch is open, no signal is provided to the corresponding input of the ECM.

* When a switch is closed, either a ground signal or +battery signal is provided to the corresponding input of the ECM.

STIC Controller

STIC Controller
(1) Downshift switch. (2) Upshift switch. (3) Direction switch.

The downshift (1), upshift (2) and direction (3) switches are components of the STIC controller and are switch inputs to the ECM. The switches are not individually serviceable. The three switches are serviced as one unit.

The purpose of the downshift switch is to tell the ECM that the operator wants the transmission to downshift one gear. The downshift switch has two input connections to the ECM; downshift N/C at connector J1 contact 25 and downshift N/O at connector J1 contact 26 of the ECM. When the operator presses the downshift switch, the downshift N/C circuit is open and the downshift N/O circuit is closed to ground. When the switch is not activated, the downshift N/C circuit is closed to ground and the downshift N/O circuit is open.

The purpose of the upshift switch is to tell the ECM that the operator wants the transmission to upshift one gear. The upshift switch has two input connections to the ECM; upshift N/C at connector J1 contact 19 and upshift N/O at connector J1 contact 23 of the ECM. When the operator presses the upshift switch, the upshift N/C circuit is open and the upshift N/O circuit is closed to ground. When the switch is not activated, the upshift N/C circuit is closed to ground and the upshift N/O circuit is open.

NOTE: The ECM requires the correct status of the two upshift and the two downshift inputs to decide when to make each shift.

The ECM does not diagnose faults on the upshift or downshift switch.

The direction switch has three positions: forward, neutral and reverse. The purpose of the direction switch is to tell the ECM which direction the operator wants the transmission in: forward, neutral or reverse. The connections to the ECM are: forward at connector J1 contact 30, neutral at connector J1 contact 13 and reverse at connector J1 contact 14. The selected position is grounded. The unselected positions are open.

NOTE: The ECM diagnoses certain failures in the circuit of the direction switch. If an invalid combination of opens and/or grounds exist, the ECM knows a circuit failure is present. The ECM will shift the transmission to NEUTRAL. This fault is then shown on the VIMS message center display; see the subject Diagnostic Operation.

NOTE: The ECM evaluates the direction switch contacts for 30 seconds before declaring a fault condition.

Lockup Clutch Enable Switch

The lockup clutch enable switch is an input of the ECM. The purpose of the switch is to tell the ECM whether or not the operator wants the lockup clutch function to operate. The ECM responds accordingly by enabling (turns ON) or disabling (turns OFF) the lockup clutch function; see the subject Electronic Torque Converter in the Additional Features section.

The lockup clutch enable switch is a two position rocker switch. When the switch is deactivated (turned off), terminal 3 is open. When the switch is activated (turned on), terminal 3 is closed to ground. Terminal 3 connects to connector J1 contact 32 of the ECM. Terminal 2 connects to frame ground.

NOTE: The ECM does not diagnose faults on this switch. The status of the lockup enable switch is available to other modules on the CAT data link.

Reduced/Max Rimpull Enable Switch

The reduced/max rimpull enable switch is an input of the ECM. The purpose of the switch is to tell the ECM whether or not the operator wants the reduced rimpull function to operate. When the switch is placed in the "reduced" position, the contact closes to +battery. The ECM responds accordingly by reducing (switch in "reduced") the available rimpull to a preset level or allowing (switch in "max") the maximum rimpull to the wheels.

NOTE: The normally open circuit of the reduced/max rimpull enable switch is used as input to the ECM. The ECM does not diagnose faults on this switch. The status of the reduced/max rimpull enable switch is available to other modules on the CAT data link.

Reduced Rimpull Selection Switch

The reduced rimpull selection switch is an input of the ECM. The purpose of the switch is to allow the operator to select one of four preset levels of maximum available rimpull. The four levels have factory default settings and may also be set with a service tool or from the monitoring system. During machine operation, the left pedal may be used to further reduce the available rimpull.

NOTE: The ECM diagnoses certain failures in the circuit of the reduced rimpull selection switch. If all four circuits are open or if more than one circuit is shorted to ground a fault is declared. This fault is then shown on the VIMS message center display; see the subject Diagnostic Operation.

Key Start Switch

The key start switch is an input of the ECM and connects to connector J1 contact 40. The purpose is to tell the ECM that the operator wants to start the engine (has placed the key start switch in the start position). The ECM then initiates the neutral start function; see the subject Neutral Start in the Additional Features section.

NOTE: After the key start switch is initially turned to the START position, the switch will not return to the START position from the ON position. The switch must first be turned to the OFF position, then it can be turned to the START position.

NOTE: The ECM does not diagnose faults on this switch. The status of the key start switch is available to other modules on the CAT data link.

Steering/Transmission Lock Switch

The steering/transmission lock switch is an input of the ECM. The purpose of the switch is to tell the ECM when the operator has the steering/transmission/lock lever in the locked position. If the transmission is NOT in neutral and the lock lever is placed in the LOCKED position, then the ECM shifts the transmission to neutral. Now, if the lock lever is moved to the UNLOCKED position, the ECM prohibits all shift requests until the operator places the direction switch (of the STIC controller) in the neutral position.

NOTE: Two circuits (N/C and N/O) for the steering/transmission lock switch are used for diagnostic purposes. If the two circuits are ever in the same state (open or grounded), the ECM knows a circuit failure is present. This fault is then shown on the VIMS message center display; see the subject Diagnostic Operation. The status of the steering/transmission lock switch is available to other modules on the CAT data link.

Quick-Shift Switch

Quick-shift Switch

The quick-shift switch is an input of the ECM. The purpose of the switch is to tell the ECM that the operator wants the quick-shift function to operate. The ECM then enables the quick-shift function; see the subject Quick-shift in the Additional Features section.

NOTE: The ECM diagnoses certain failures in the circuit of the quick-shift switch. If the two circuits are ever in the same state (open or grounded), the ECM knows a circuit failure is present. This fault is then shown on the VIMS message center display; see the subject Diagnostic Operation. The status of the quick shift switch is available to other modules on the CAT data link.

Parking Brake Pressure Switch

The parking brake pressure switch is an input of the ECM. The purpose of the switch is to provide the ECM with information on the hydraulic portion of the parking brake assembly. The parking brake is spring applied and hydraulic pressure released. When the parking brake pressure switch is not actuated (no pressure in the hydraulic portion of the assembly), the parking brake is "ON". When the switch is actuated (pressure present in the hydraulic portion of the assembly), the parking brake is "OFF".

NOTE: Two circuits (N/C and N/O) for the parking brake pressure switch are used for diagnostic purposes. If the two circuits are ever in the same state (open or grounded), the ECM knows a circuit failure is present. This fault is then shown on the VIMS message center display; see the subject Diagnostic Operation. The status of the parking brake pressure switch is available to other modules on the CAT data link.

Neutralizer Pressure Switch

The neutralizer pressure switch is an input of the ECM. The purpose of the switch is to provide the ECM with information on the operation of the left pedal. When the neutralizer pressure switch is not actuated, the left pedal is released. When the neutralizer pressure switch is actuated (pressure present in the hydraulic portion of the assembly), the left pedal is depressed.

NOTE: Two circuits (N/C and N/O) for the neutralizer pressure switch are used for diagnostic purposes. If the two circuits are ever in the same state (open or grounded), the ECM knows a circuit failure is present. This fault is then shown on the VIMS message center display; see the subject Diagnostic Operation.

Sensors

Sensors provide information (input) to the ECM about changing conditions, such as speed and position. The sensor signal changes in a proportional manner to reflect the changing condition. The type of sensor signals that the ECM recognizes are:

* Frequency - The sensor produces a signal in which the frequency (Hz) varies as the condition changes.

* Pulse width modulated (PWM) - The sensor produces a signal in which the duty cycle varies as the condition changes. The frequency of this signal is constant.

Frequency Sensors

Frequency sensors produce a signal in which the frequency (Hz) varies as the condition changes.

Transmission Output Speed Sensor

Transmission Output Speed Sensor - Input

The transmission output speed sensor is an input of the ECM. The purpose of the sensor is to allow the ECM to determine the transmission speed. The ECM combines the transmission output speed with several other machine conditions to diagnose transmission output speed problems. The transmission output speed and diagnostic status of the sensor are available to other modules on the CAT data link.

The transmission speed output sensor is used to measure transmission output RPM. The speed sensor is a frequency sensor. This sensor generates a sine wave signal, from passing gear teeth, which is sent to the ECM. The ECM measures the signal frequency (one pulse per gear tooth) and determines the transmission output speed.

The signal wire (connector contact C) of the transmission output speed sensor connects to connector J2 contact 35 of the ECM. The sensor is supplied operating power (+10V) at connector contact A from the ECM (connector J2 contact 9). The speed sensor return (connector contact B is connected to connector J2 contact 24 of the ECM.

Torque Converter Output Speed Sensor - Input

Torque Converter Output Speed Sensor

The torque converter output speed sensor is an input of the ECM. The purpose of the sensor is to allow the ECM to determine the torque converter output speed. The torque converter output speed and diagnostic status of the sensor are available to other modules on the CAT data link.

The torque converter output speed sensor is used to measure torque converter speed and direction. The speed sensor is a frequency sensor. This sensor generates a repeating pattern, from passing rotor teeth, which is sent to the ECM. The ECM measures the signal frequency (one pulse per rotor tooth) and determines the torque converter speed and direction.

The signal wire (connector contact C) of the torque converter output speed sensor connects to connector J2 contact 38 of the ECM. The sensor is supplied operating power (+10V) at connector contact A from the ECM (connector J2 contact 9). The speed sensor return (connector contact B is connected to connector J1 contact 15 of the ECM.

Pulse Width Modulated (PWM) Sensors

Pulse Width Modulated Signal

Typical PWM Sensor Schematic

Pulse width modulated (PWM) sensors produce a digital signal in which the duty cycle varies as the condition changes. The frequency remains constant.

Impeller Clutch Pressure Sensor

The impeller clutch pressure sensor is an input of the ECM. The purpose of the sensor is to determine the pressure of the torque converter impeller clutch. The impeller clutch pressure sensor is a pulse width modulated input signal to the ECM. The final impeller clutch pressure is available to other modules on the CAT data link.

The signal wire (connector contact C) of the impeller clutch pressure sensor connects to connector J2 contact 6 of the ECM. The sensor is supplied operating power (+8) at connector contact A from the machine electrical system. Connector contact B of the sensor is connected to frame ground.

Torque Converter Oil Outlet Temperature Sensor

The torque converter oil outlet temperature sensor is an input of the ECM. The purpose of the sensor is to determine the temperature of the torque converter oil. The torque converter oil outlet temperature sensor is a pulse width modulated input signal to the ECM. The final torque converter oil outlet temperature is available to other modules on the CAT data link.

The signal wire (connector contact C) of the impeller clutch pressure sensor connects to connector J2 contact 5 of the ECM. The sensor is supplied operating power (+8) at connector contact A from the machine electrical system. Connector contact B of the sensor is connected to frame ground.

Transmission Clutch Solenoid Valves

Clutch Solenoid Valve Identification

Transmission Clutch Solenoid Valve

The transmission clutch solenoid valves are outputs of the ECM. The purpose of the solenoid valves is to direct pilot oil to the ends of the control spool. The control spool will shift allowing pressure oil to the corresponding clutches. Based on the operators request from the STIC controller, the ECM activates the appropriate transmission clutch solenoid valves. A transmission clutch solenoid valve is energized by a PWM signal sent by the ECM. Clutch solenoid valves 1 and 2 are for direction. Clutch solenoid valves 3, 4 and 5 are for speed. For movement of the machine two clutch solenoid valves are activated; one for direction and one for speed. When the transmission is in neutral, only clutch solenoid valve 3 is activated.

The clutch solenoid valves have a connector with two contacts. One contact receives power from the corresponding connector, clutch 1 J1-17, clutch 2 J1-11, clutch 3 J2-7, clutch 4 J2-1 and clutch 5 J2-8 of the ECM. The other contact of all solenoid valves join together and return to connector J1 contact 7 or connector J2 contact 3 of the ECM. Diagnostic status of the solenoids is available to other modules on the CAT data link.

With the clutch solenoid valves a pulse and hold strategy is used to extend the life of the coil of the solenoid valves. The ECM has the capability of controlling the amount of current from the output. For ON/OFF type solenoids, the current needed to get a solenoid to engage is much higher than the current needed to keep the solenoid engaged. The pulse and hold strategy makes use of this characteristic of a solenoid by setting the current to the solenoid to maximum and then reducing the current to a lower level after one second. Lowering the current to the valve reduces the heat that is dissipated by the coil of the solenoid.

NOTE: The solenoid coils are not designed for direct 24 DCV operation. The ECM sends a 24 volt PWM signal at a duty cycle which provides an average voltage of about 8 to 12 volts to the solenoid coils. Do NOT activate the coils with 24 DCV (+battery) or the life of the coils will be drastically reduced. If the coils must be activated by means other than the ECM, use a 12 DCV source.

NOTE: Engagement of the neutral clutch is delayed two seconds from the time the operator selects neutral. During this delay, the transmission is in a "no clutch neutral" state, with none of the transmission clutch solenoid valves energized. This "no clutch neutral" state is provided in order to improve the quality of directional shifts. The ECM momentarily prevents the engagement of the neutral clutch as the operator changes from forward to reverse (or reverse to forward) direction.

Torque Converter Solenoid Valves

Impeller Clutch And Lockup Clutch Solenoid Valves (Lockup Clutch Solenoid Valve Is Shown)

The impeller clutch solenoid valve is an output of the ECM and functions as a reducing valve. The purpose of the solenoid valve is to modulate the hydraulic pressure of the impeller clutch. When the ECM increases the current to the solenoid valve, hydraulic pressure at the impeller clutch is reduced; when the current is zero, the impeller clutch pressure is maximum. The ECM varies the current (PWM signal) to the solenoid valve and the solenoid valve modulates the impeller clutch pressure.

The lockup clutch solenoid valve is an output of the ECM and functions as a proportional valve. The purpose of the solenoid valve is to activate or deactive the lockup function (direct drive). When the ECM sends a high current (high duty cycle) signal to the solenoid valve, the lockup function is activated. With a high current there will also be a high pressure to the lockup clutch when activated. When the ECM does not send a current signal to the solenoid valve, the lockup function is deactivated.

The lockup and impeller clutch solenoid valves are part of a valve body located on the torque converter. The solenoid valves have a connector with two contacts. Connector contact 1 of the solenoid valve receives power from the ECM. ECM connector J2 contact 13 provides power to the lockup clutch solenoid valve. ECM connector J2 contact 19 provides power to the impeller clutch solenoid valve. Connector contact 2 of all solenoid valves join together and return to connector J1 contact 7 or connector J2 contact 3 of the ECM.

NOTE: The solenoid coils are not designed for direct 24 DCV operation. The ECM sends a 24 volt PWM signal at a duty cycle which provides an average voltage of about 12 volts to the solenoid coils. Do NOT activate the coils with 24 DCV (+battery) or the life of the coils will be drastically reduced. If the coils must be activated by means other than the ECM, use a 12 DCV source.

NOTE: The lockup and impeller clutch solenoid valves are very different mechanically, although they appear the same. The two solenoid valves must not be switched mechanically or electrically.

Air Start Solenoid

The air start solenoid is an output of the ECM. The purpose of the air start solenoid is to turn on and off the air starting motor. The ECM checks to make sure the direction switch is in NEUTRAL and battery voltage is less than 32 volts. If these starting conditions are satisfied, the ECM sends a +battery signal (connector J1 contact 8) to the air start solenoid and engine cranking begins. See the subject Neutral Start in the Additional Features section.

The air start solenoid has a connector with two contacts. One contact receives power from connector J1 contact 8 of the ECM. The other contact (along with the other ECM outputs) returns to connector J1 contact 7 or connector J2 contact 3 of the ECM.

NOTE: Faults are shown on the VIMS message center display; see the subject Diagnostic Operation. The status of the air start solenoid is available to other modules on the CAT data link.

Backup Alarm Relay

The backup alarm relay is an output of the ECM. The purpose of the backup alarm relay is to energize the dual backup alarms, making nearby personnel aware that the machine is backing up. When the operator selects REVERSE, the ECM activates the backup alarm relay. When activated the backup alarm relay receives +battery from the ECM.

The backup alarm relay has two terminals for electrical connections. One terminal receives power from connector J2 contact 37 of the ECM. The other contact (along with the other ECM outputs) returns to connector J1 contact 7 or connector J2 contact 3 of the ECM.

NOTE: Faults are shown on the VIMS message center display; see the subject Diagnostic Operation. The status of the backup alarm relay is available to other modules on the CAT data link.

Data Link

The data link is an input and an output of the ECM; at connector J1 contacts 3 and 9 of the ECM connector. The purpose of the data link is to communicate with other electronic control modules on the machine. The data link is not a visible component; it consists of internal ECM circuits and the connecting harness wiring. The data link is bidirectional which allows the ECM to receive and send information.

Caterpillar Electronic Technician (ET) also communicates with the ECM's over the data link. After communication has been established, ET will list the ECM's on the machine and the diagnostic information that is available.

All electronic ECMs that use the data link have a module identifier (MID). The MID for the power train ECM is the number 081.

Normal Operation

The primary duty of the ECM is to electronically control the shifting of the transmission. The ECM activates the appropriate clutch solenoid valves to engage the transmission gear that is requested by the STIC controller. The basic components and corresponding requirements for shifting are listed below. (also see Exceptions):

* STIC Controller - The direction, upshift and downshift switches, located in the STIC controller, tell the ECM the requests of the operator; forward, reverse, neutral, upshift or downshift. The ECM acts upon the shift requests by activating the appropriate transmission clutch solenoid valves. Except for certain conditions, the ECM shifts the transmission as requested by these switches; also see the subject Exceptions.

* Transmission Clutch Solenoid Valves - These clutch solenoid valves, located on the transmission, direct pilot oil to the ends of the control spool. The control spool will shift allowing pressure oil to the corresponding clutches. The ECM decides which clutch solenoid valves to activate, based on the input from the direction, upshift and downshift switches (STIC controller). Clutch solenoid valves 1 and 2 are for direction. Clutch solenoid valves 3, 4, and 5 are for speed. For movement of the machine two clutch solenoid valves are activated; one for direction and one for speed. When in neutral, only clutch solenoid valve 3 is activated.

Exceptions

These are the exceptions to normal shifting as previously described in the Normal Operation section.

* If the upshift and downshift switches of the STIC controller are pressed at the same time, then the ECM does not shift the transmission.

* If the steering/transmission lock lever is placed in the LOCKED position (lock switch activated) when the transmission is NOT in neutral, then the ECM shifts the transmission to neutral. The ECM does not allow other shifts until the steering/transmission lock lever is placed in the UNLOCKED position (lock switch deactivated) and the direction switch is placed in the NEUTRAL position.

Additional Features

These are the features that are in addition to normal shifting as previously described in the Normal Operation section.

No Clutch Neutral

The no clutch neutral feature is provided in order to improve the quality of directional shifts. This feature momentarily prevents the engagement of the neutral clutch as the operator changes from forward to reverse (or reverse to forward) direction. The ECM delays engagement of the neutral clutch for two seconds from the time the operator shifts into or through neutral. During this delay, none of the transmission clutch solenoid valves are energized.

Quick-Shift

The quick-shift feature is intended to help an operator with a loading cycle that has a high percentage of second gear operation. The operator turns this feature on and off with the quick-shift switch.

With the quick-shift switch activated and the transmission in first forward, the ECM shifts the transmission to second reverse when the direction switch is moved to reverse from forward. When the direction switch is moved back to forward, the ECM shifts the transmission from second reverse to second forward. The operator must then downshift to first forward and the quick-shift cycle can be repeated.

NOTE: The quick-shift feature only functions when the transmission is in first forward and the quick-shift switch is ON.

Neutral Start

The neutral start feature requires the STIC controller direction switch to be in the NEUTRAL position before the engine will crank. The operator controls this feature by placing the direction switch in the neutral position and turning the key start switch to the START position. The purpose of this feature is to allow engine starting only when the transmission is in neutral. When this feature is in operation, the ECM activates the start relay allowing the starting motor to turn.

NOTE: Battery voltage must be less than 32 volts to start.

Backup Alarm

The backup alarm feature is enabled when the operator places the direction switch in the reverse position. The purpose of this feature is to alert personnel that the machine is backing up. When this feature is operating, the ECM activates the backup alarm relay which activates the dual backup alarms.

Gear Indicator

(1) Gear indicators.

The active gear of the transmission is visible on the instrument panel.

Parking Brake Interlock

The parking brake interlock is used to prevent accidental or unintended movement of the machine and to prevent the operator from unintentionally driving through the parking brake.

When the parking brake is engaged, the transmission will not shift into first forward or reverse. If the transmission is in first forward or reverse when the parking brake is set, the ECM will shift the transmission to first neutral. If the STIC input switches are set to first gear, direction switch forward or reverse, when the operator releases the parking brake, the transmission will not shift into gear until the operator selects neutral and then forward or reverse. Second and third gears are provided as needed for drive train service procedures.

Parking Brake Drive Through

This allows the machine to be moved when parking brake release pressure is not available.

If parking brake release pressure is not available, the spring applied parking brake will engage. If the machine is traveling in 2nd or 3rd gear, the transmission will remain in forward or reverse. If the machine is traveling in 1st gear, the transmission will be shifted into neutral. In both cases, the machine will come to a stop, due to the parking brake.

If the transmission is in neutral when the parking brake pressure is lost, an operator request to shift into forward or reverse will be ignored. The VIMS monitoring system will indicate that the parking brake is engaged with a Category 1 warning. The operator may drive through the parking brake by placing the direction switch in neutral and then moving the switch to the direction identical to the first request. On this second attempt to move the machine with the parking brake engaged, the ECM will shift the transmission to the requested gear.

Electronic Torque Converter

The electronic torque converter feature consists of the lockup clutch function and the impeller clutch function. The two functions operate independently.

Lockup Clutch Function

The lockup clutch function electrically controls direct drive. When the ECM activates the lockup clutch solenoid valve, the lockup clutch within the torque converter mechanically connects the torque converter input shaft to the torque converter output shaft. The purpose of this function is to engage or disengage the torque converter lockup clutch in response to various operating conditions. This provides better machine performance during roading or load and carry operation.

The torque converter lockup clutch control inputs are:

* Speed and direction handle switches.

* Lockup clutch enable switch.

* Torque converter output speed.

* Service brake status.

* Left pedal status - neutralizer pressure switch.

For faults on any of the above inputs, the lockup clutch will be disengaged.

When the lockup clutch is first commanded on, the lockup clutch solenoid current is brought to a hold level for 0.75 seconds to allow the clutch to fill. The current is then ramped to full on in .65 seconds. The control will have the following specifications:

* Impeller clutch pressure will remain at full pressure when the torque converter lock up clutch is engaged.

* Torque converter lockup clutch will engage when the lockup enable switch is in the enable position, and torque converter output speed is greater than or equal to 1125 RPM.

* The lockup clutch will disengage when the lockup enable switch is moved to the off position or torque converter speed is less than or equal to 975 RPM.

* Torque converter lock up clutch will disengage for all directional and speed shifts. The lockup clutch will be re-enabled 2 seconds after the start of the shift.

* Torque converter lock up clutch will not engage if torque converter speed is above 1750 RPM.

* The torque converter lockup clutch will disengage when the operator depresses the left pedal or the service brake (right) pedal.

* The control will disengage the torque converter lockup clutch on high vehicle deceleration to prevent engine lug down when engaging the pile.

The torque converter lockup clutch will re-enabled for 4 seconds after the following:

* Service brake pedal is released.

* Service brake pedal information fault is cleared.

* Left pedal is released (neutralizer pressure switch).

* Torque converter lockup clutch fault is cleared (neutralizer pressure switch fault).

* Lockup enable switch off-to-on transition.

* Rapid converter speed drop.

* Low torque converter output speed fault.

NOTE: While using the brakes during rapid deceleration of the machine, the lockup clutch will be disengaged when application of the service brake is communicated from the engine ECM over the CAT data link.

NOTE: The lockup clutch will not be engaged when the transmission is placed into first forward. All other transmission gears will allow the LUC to be engaged when the LUC enable switch is in the enable position.

Impeller Clutch Function

Left Pedal - The position of the left pedal is used to determine the impeller clutch pressure. Depressing the left pedal reduces the impeller clutch pressure, which makes more engine power available (for implement and steering systems) and also reduces maximum rimpull (allows the operator to control wheel slippage). Fully depressing the left pedal engages the service brakes.

Reduced Rimpull Control - There is also an additional rimpull feature that allows the operator to select the amount of impeller clutch pressure reduction to one of four preset levels. The amount of impeller clutch pressure is selected using the reduced rimpull selection switch. This feature is enabled when the reduced/max rimpull enable switch is in the ON position and the transmission is in first forward, neutral, or reverse. If the left pedal is depressed with the reduced rimpull feature ON, the impeller clutch pressure will be dropped to neutralize the transmission. With this switch in the OFF position the amount of rimpull available is 100 percent.

The four impeller clutch pressure reduction percentages are preset at the factory to 45, 55, 70 and 85. These pressures can be changed using SERV (7378) mode of VIMS or ET. For more information, see the heading Enter Calibration Modes under the subject Service Operations.

Position 1 (large dot) of the reduced rimpull selection switch is always the largest amount of impeller clutch pressure (rimpull) and position 4 (smaller dot) is the least. If the programmed values are corrupted for any reason, the ECM resets the values to the factory default settings.

Directional Shifts - When the operator requests a directional shift, the ECM:

1. When the shift begins, the impeller clutch pressure is reduced and maintained at a hold value of 550 ± 207 kPa (80 ± 30 psi).

2. When the ECM determines that the transmission clutches have engaged the impeller clutch pressure is increased to a maximum value, about 2584 ± 207 kPa (375 ± 30 psi). This maximum impeller clutch pressure is maintained for one second, then reduced to about 2274 ± 207 kPa (330 ± 30 psi). This pressure is known as the top pressure.

3. The impeller clutch pressure is increased to maximum pressure to ensure that the impeller clutch engages quickly, but once it has engaged, impeller clutch pressure is reduced to extend impeller clutch seal life. The top value is maintained until conditions (left pedal position, engine speed, lockup clutch engaged) require a change of impeller clutch pressure.

Engine Response Function

To increase engine and machine response during engine acceleration from low idle, the impeller clutch operates as follows:

* During the progression from low idle to 1100 RPM, the impeller clutch pressure is maintained at the fill value of 551 ± 207 kPa (80 ± 30 psi).

* During the progression from 1100 to 1300 RPM, the impeller clutch pressure is gradually increased to the maximum value. The top value is maintained until conditions (left pedal position, engine speed, rimpull control) require a change of impeller clutch pressure.

Reverse Turbine Function

High temperatures of the impeller clutch can be produced when the machine is allowed to move backward while on an incline and a forward gear is engaged. The reverse turbine function reduces the temperatures that are created when the machine is operated in this manner. If the torque converter speed is greater than 500 RPM in a reverse direction, the ECM increases the impeller clutch pressure and the left pedal is ignored. (Braking is not affected.)

Engine Speed Controlled by the Power Train ECM

At times, engine speed is determined by the power train ECM. The power train ECM regulates engine speed to provide controlled throttle shifting. The power train ECM sends a transmission requested engine speed limit to the engine ECM by means of the CAT data link. Once the engine ECM receives the transmission requested engine speed limit, this speed is compared to the other engine speed inputs, like the throttle pedal. The engine ECM compares these speeds and selects the lowest one to use as the desired engine speed. The engine ECM then controls the fuel delivery to the engine to try to achieve the desired engine speed.

ET is especially useful in troubleshooting problems with these features. With ET, the parameters used by the ECM's to perform these features can be viewed and problems quickly identified.

Controlled Throttle Shifting (A Failure Mode)

Enabled during a direction shift when any of the following faults are active.

Controlled throttle shifting is activated when an electrical fault is detected on the torque converter impeller clutch solenoid valve circuit. Once activated, the power train ECM sends a transmission requested engine speed limit to the engine ECM to control engine speed during transmission directional shifts. The purpose of this feature is to reduce the energy absorbed by the directional clutches during a direction shift. This allows the machine to be operated without the impeller clutch until a repair can be made.

When a direction shift is requested and a fault is active, the power train ECM sends a transmission requested engine speed limit of 1100 rpm to the engine ECM by means of the CAT data link. The power train ECM will hold this engine speed request for 1.9 seconds if shifting into forward, and 2.5 seconds if shifting into reverse.

Direction shifts made at engine speeds below 1100 rpm are not affected by this strategy.

Engine Pre-lube

This function is used to command the engine ECM to perform a pre-lube cycle at machine start-up.

At power up the power train ECM requests pre-lube status from the engine ECM up to four times. The normal response for an engine with the pre-lube attachment is a status of "off". If the engine does not have the pre-lube attachment, the engine ECM will respond with a status of "disabled". If there is no response from the engine ECM, the CAT data link is assumed to be inoperable and the status is assumed to be "disabled". The ECM records the status information. If the stored status is "disabled", the engine pre-lube is disabled.

The engine ECM will decide if a pre-lube cycle is required. If a pre-lube cycle is required, the engine ECM responds with a pre-lube status of "on". If a pre-lube cycle is NOT required, the engine ECM responds with a pre-lube status of "off".

If the pre-lube status received from the engine ECM is "off", the pre-lube function returns control to the neutral start function to start the engine.

If the request for pre-lube status has failed three times, the pre-lube function waits 3.8 seconds and then returns control to the neutral start function to start the engine.

Programmable Top Gear

ET Screen For Transmission 994D Configuration

The Caterpillar ET service tool must be used to set the maximum allowed transmission gear for each direction and all operating conditions. In ET, go to the "Service" icon and select the "Configuration Screen" to change either "Transmission Maximum Forward Gear" or "Transmission Maximum Reverse Gear". The ECM will initially default to third forward and third reverse. A tattletale count will also be incremented and stored each time the maximum gear is changed.

Power Train Condition Indication

The power train condition indication is used to provide the machine operator and service personnel reasons the machine is not operating as normally expected.

The ECM continuously monitors the power train control for many diagnostic conditions. As an aid to service personnel using ET or VIMS, the following three classes of power train conditions are available on the CAT data link:

* Shutdown - These conditions indicate the reason for transmission operation being shutdown.

* Derate - These conditions indicate the reason for the transmission to be operating in a derated or modified mode.

* Status - These conditions indicate various transmission modes of operation that are related to shutdown or derate.

Power Train Shutdown Indicator

* Low System Voltage - This shutdown indicates that the power supply voltage to the ECM is below the low voltage limit of 18 volts.

* High System Voltage - This shutdown indicates that the power supply voltage to the ECM is above the high voltage limit of 32 volts.

* Multiple Sol Faults - This shutdown indicates that a fault is present for more than one transmission solenoid. The ECM constantly diagnoses short to battery and short to ground faults for all transmission speed and direction solenoids.

* Strg/Trans Lock ON - This shutdown indicates that the steering transmission lockout switch is in the locked out position.

* Latched to Neutral - This shutdown indicates that the transmission has been automatically shifted to neutral due to one of the following:

Steering/Transmission Lock Switch In Lock Position

Parking Brake Engaged In First Gear

Fault On Direction Switch

Impeller Clutch Solenoid Shorted To +Battery

Starter Relay Shorted To +Battery

Key Switch In Start Position When The

Transmission Is Not In Neutral

The operator is required to move the direction switch to the neutral position before a direction shift may be attempted.

* Trans Solenoids Disabled - This shutdown indicates that all of the transmission solenoids have been disabled due to one of the following:

High System Voltage

Multiple Solenoid Faults

Low System Voltage While In Neutral

* Starter Disabled - This shutdown indicates that the operator has moved the key start switch to the start position and the starter is disabled due to the following:

Shift Lever Not In Neutral

High System Voltage

Power Train Derate Indication

* TC Implr Sol Derate - This derate is the result of a diagnosed fault on the torque converter impeller clutch solenoid. This derate condition results in controlled throttle shifting.

* TC Implr Press Derate - This derate is the result of energizing the torque converter impeller clutch solenoid and detecting little change in the impeller clutch pressure. The impeller clutch is assumed to be defective. This derate condition results in controlled throttle shifting.

* Neutral Shift Inhibit - This derate results from attempting to shift to neutral when the machine is traveling above the neutral shift speed limit.

* Speed Sensor Derate - This derate results from a fault condition on the torque converter output speed or transmission output speed sensor.

Power Train Status Indication

* CTS Active - This status indicates that controlled throttle shifting is active.

* Reduced Rimpull Active - This status indicates that operating conditions are correct for Reduced Rimpull Mode to be active.

* Engine Prelube Active - This status indicates that an engine prelube operation is currently in progress.

* Timed IC Active - This status indicates that the timed IC Mode is active for direction shifts. This mode is the result of a speed sensor or sensor supply fault.

* Not In Neutral - This status indicates that the starter is disabled due to the transmission or shift lever not in neutral.

* Top Gear Limit - This status indicates an upshift switch has been held depressed while the transmission is currently in the top gear limit speed range. The status will not be active when the transmission is in the factory default speed range.

* LUC Disabled - This status indicates that lockup clutch operation is disabled due to one of the following conditions:

Fault Exists For The Neutralizer Pressure Switch

Fault Exists For The Service Brake Pedal Information

Lockup Clutch Solenoid Is In A Failure Mode

Torque Converter Speed Is Above The Set Limits

The status may only be active if the lockup enable switch is in the ON position.

* Parking Brake Lockout - This status indicates that the parking brake has been engaged while the machine was operating in first gear forward or reverse.

* Active Diagnostic - This status indicates that an active diagnostic pertaining to one of the shutdown or derate conditions is present.

* Key Start Switch In Start - This status provides information for the Latched to Neutral Power Train Shutdown Indicator.

Event Logging

ET Screen For Logged Event Codes

The purpose of event logging is to identify machine operating conditions, which have the potential of damaging the transmission, or other components associated with the power train. The Caterpillar ET service tool must be used to view and clear each event in the table.

Event Description

* Coasting In Neutral Warning - This event is logged when the machine is in neutral with ground speed above 110 km/h (6.2 mph) for at least two seconds. Only one occurrence of the event is possible until the machine is put in gear and brought back to neutral. If the ground speed drops below 10 km/h (6.2 mph), then increases again, the event will no be logged again. This will prevent the appearance of multiple occurrences of the event when ground speed is around the threshold level.

* High Speed Directional Shift - This event is logged when ground speed is greater than 14 km/h (8.7 mph) and a direction shift is requested by the operator.

* Low Torque Converter Oil Temperature - This event is logged when ground speed is greater than 1 km/h (.6 mph) for 30 seconds while the torque converter temperature is less than 40°C (104.0°F). An event will not log every time the ground speed drops below the threshold and increases again or the temperature rises and then decreases below the threshold unless the ground speed becomes equal to zero (machine stopped). This will prevent the appearance of multiple occurrences of the event when the triggering conditions are near the threshold level.

* High Torque Converter Oil Temperature - This event is logged when ground speed is greater than 1 km/h (.6 mph) for 30 seconds while the torque converter temperature is greater than 132°C (270.0°F). An event will not log every time the ground speed drops below the threshold and increases again or the temperature drops below the threshold and increases again unless the ground speed becomes equal to zero (machine stopped). This will prevent the appearance of multiple occurrences of the event when the triggering conditions are near the threshold level.

* Excessive Sustained Third Gear Operation - This event is logged when the machine has been operated in third gear with the ground speed greater than 13 km/h (8.1 mph) continuously for 8 minutes.

* Machine Driven With Parking Brake On - This event is logged when ground speed is greater than 1 km/h (.6 mph) with the parking brake engaged. This event will log every time the parking brake is engaged for at least 1 second while the machine is traveling forward or backward at a speed greater than 1 km/h (.6 mph) or if the machine is driven for longer than 1 second without removing the parking brake. An event will not log every time the ground speed drops below the threshold and increases again unless the parking brake is released, then reengaged. This will prevent the appearance of multiple occurrences of the event when ground speed is around the threshold level.

Diagnostic Operation

The ECM detects faults that occur in most of the input and output circuits. A fault is detected when the signal (at the contact of the ECM) is outside a valid range. The ECM then records the fault. If the fault goes away (not present), the fault information remains stored for 150 service hours in the ECM until cleared in VIMS or by ET.

The diagnostics of the ECM are available to assist with the troubleshooting of detected faults. A service code is used to specify each detected fault. The service code consists of three identifiers (MID, CID and FMI). The service code is shown in the message area of VIMS. Faults can also be viewed with ET. The identifiers are:

* Module Identifier (MID) - The MID is a three digit code shown on the display area. The MID is displayed with the service code. The MID tells which ECM diagnosed the fault. Some MID's are:

Engine ECM ... 036

VIMS Main Module ... 049

VIMS I/M #1 ... 057

VIMS I/M #2 ... 058

Power Train ECM ... 081

NOTE: The MID of the power train ECM is 081. When troubleshooting the power train system, make sure the number 081 appears with the service code of the fault. VIMS also shows service codes of faults that are not related to the power train system. The MID number 081 identifies the service code as coming from the power train ECM.

* Component Identifier (CID) - The CID tells which component or circuit is faulty. For example; start relay or reverse solenoid. The CID is a three digit code shown on the display area. The MID, CID and FMI are displayed together.

* Failure Mode Identifier (FMI) - The FMI tells what type of failure has occurred. For example; voltage above normal, current below normal or abnormal frequency. The FMI is a two digit code shown on the display area. The MID, CID and FMI are displayed together.

NOTE: For a list of CID and FMI codes for the power train ECM, see the Service Codes chart under the topic Troubleshooting Faults With Service Codes in the Testing And Adjusting section.

The power train ECM does not have a display area for showing diagnostic information to service personnel. Diagnostic information concerning the power train system is sent on the CAT data link to VIMS and ET. Service personnel must be familiar with VIMS and ET in order to troubleshoot the power train system.

EACK and ELIST of VIMS allows service personnel to see and to troubleshoot the faults that the power train ECM has detected. While VIMS is in EACK or ELIST, the fault or service code for any detected fault of the power train ECM is shown in the display area of VIMS.

NOTE: Active diagnostic codes may also be viewed with the ET service tool. Logged diagnostic codes may be reviewed and cleared by service personnel during machine maintenance using ET.

For more information, see "Troubleshooting System Events" in the Testing And Adjusting portion of this manual to troubleshoot the faults for the power train ECM.

VIMS Normal Operation

Message Center Module
(1) Alert indicator. (2) Data logging indicator. (3) Message area. (4) Universal gauge. (5) Gauge warning area.

This section contains a brief overview of the VIMS system. The purpose of this section is to provide the information required to:

* Get diagnostic fault codes.

* Run service procedures.

* Clear fault codes.

NOTE: For a full description of the VIMS system see Service Manual SENR6059.

During normal operation, the VIMS display components show the operator and service person:

* Whether VIMS is operating properly. Whenever the key start switch is turned to the ON position, some VIMS outputs (message center module) briefly operate. VIMS is performing a test. For a complete test of the VIMS outputs, see the topic Self Test.

* A value for system condition. VIMS continuously watches machine systems.

* Whether a machine abnormal system condition (data event) exists. VIMS continuously watches machine systems. When an abnormal condition (problem) exists, alert indicator (5) FLASHES and message area (7) shows what system parameter has an abnormal condition and what the condition is. Universal gauge (8) also shows the approximate value of the abnormal parameter. The event is stored in the main module memory. As the severity of the problem increases the action lamp FLASHES and the action alarm SOUNDS. See Warning Operation section.

* Whether an electrical system fault exists, VIMS continuously checks for electrical faults in VIMS and other electronic control module systems (engine, power train, etc.) on the machine. When a maintenance fault is detected, the fault is shown on the message area and stored in the main module memory. See Service Operations section.

VIMS enters normal mode when it is powered-up (key start switch turned on). Leaving normal mode is done by: initiating a service operation with the keypad. See Service Operations section.

Service Operations

There are numerous VIMS service operations that can be initiated by the operator or service person. Each service operation is assigned a service program code (SPC). This service program code is entered into VIMS using the keypad. Entering the service program code initiates the corresponding service operation. Some of the service operations are:

NOTE: For a complete explanation of the service program code operations not found in this manual, see service manual SENR6059 "Vital Information Management System (VIMS)".

Each service program code is a unique number of one to ten digits. The service program codes have a letter equivalent that describes the service operation. This letter equivalent makes it easier to remember the service program code for each operation. The English letter equivalent for each service program code is shown in parentheses. These codes are the same regardless of the on-board language.

After entering the service program code on the keypad it must be completed by pressing the OK key within five seconds after entering the last SPC character.

Show Acknowledged Events

Service program code: 3225 (EACK)

This service program code shows all active data events and system faults that have been acknowledged but not corrected.

Show Event Statistics

Service program code: 37828 (ESTAT)

This service program code shows the number of maintenance events and data events since the main module memory was last cleared of all events (event list). Example:

Show Event List Contents

Service program code: 35478 (ELIST)

This service program code shows the event list in an abbreviated form. Event list entries are displayed on a last in - first out basis. "Out" represents when the event went deactive or turned off. This means some events may appear out of order based on their start times. Use the BACKWARD and FORWARD arrow keys to scroll through the list. The message "END OF LIST" is shown when the oldest event in the list is reached.

Data Events

For each data event in the event list, the following information is shown in the VIMS message area:

* Fault parameter name

* Fault parameter status

* Service meter reading when event began

* Event duration (VIMS only)

Example: Data event - sensor information

Example: Data event - switch information

245.2 is the service meter reading when the event began. 000:04:13 is the duration of the event in HHH:MM:SS format.

When viewing a data event, pressing the F1 key replaces what is shown on the second line of the message area with the fault parameter value and units. See F1 Key under the topic Keypad for additional information. Pressing the OK key puts the message center back in the previous mode.

Maintenance Events

For each maintenance event in the event list, the following information is shown in the VIMS message area:

* Fault name

* Fault status

* Service meter reading when event began

* Event duration (VIMS only)

Example: Maintenance event - sensor information

245.2 is the service meter reading when the event began. 000:04:13 is the duration of the event in HHH:MM:SS format.

When viewing a maintenance event, pressing the F1 key replaces what is shown on the second line of the message area with MID, CID and FMI diagnostic information. See F1 Key under the topic Keypad for additional information.

The FORWARD and BACKWARD arrow keys are used to scroll through the event list.

Toggle Display Language

Service program code: 52 (LA)

This service program code toggles the information shown on the message area between two available languages. Information is shown in the selected language until the other language is selected.

Toggle Display Units

Service program code: 86 (UN)

This service program code toggles the data shown on the display, between U.S and Metric units of measure. Data is shown in the selected units until the other units are selected.

Machine Status

Service program code: 67828 (MSTAT)

NOTE: All screens are English only.

This service program code is used to view various sections of the machine status. The message area will show the version of the source code, configuration code, experiment number, and Information Builder version (ISB).

Pressing the right arrow key will allow other aspects of the machine status to be displayed (in the following order). They and their corresponding message area display are as follows:

* Hardware Version

* Model Number

* SERIAL NUMBER (MACHINE)

* Equipment Number

* Attachment Code

Used on large wheel loaders, to identify attachments on the machine.

* Language

* Configuration Type

* Operator ID

Enter Calibration Modes

Service program code: 7378 (SERV)

This service program code is used to access the calibration modes and procedures defined in VIMS. The left or right arrow can be used to scroll through the various calibration modes. The message display will show:

Other message area displays available are:

* TC IMPLR SOL - CAL

* REDUCED RIMPULL - SET

NOTE: If OK is pressed, the phrase stays on display 15 seconds even if OK is pressed again.

Start/Stop Data Logging

Service program code: 3564 (DLOG)

This service code starts or stops data logging until 30 minutes of information is stored. (If the data logger data is being downloaded, data logging can't be started.) When stopped, the data logger indicator dots in the upper right hand corner of the universal gauge stop scrolling. These dots do not scroll when the service tool starts the data logger. When started, the remaining data logging storage time is shown on the message area for five seconds. The format of the time shown is "minutes:seconds". Example:

After showing this message, the message area shows the information that was shown before the data logging service operation was started. When data logging is in operation a series of dots scroll in the upper right hand corner of the universal gauge.

NOTE: The dots in the upper right corner of the universal gauge are shown only if data logging is started from the keypad.

Warning Operation

Message Center Module
(1) Alert indicator. (2) Data logging indicator. (3) Message area. (4) Universal gauge. (5) Gauge warning area.

VIMS notifies the operator of an immediate or impending problem with a machine system. Warning operation begins when VIMS receives a problem signal that reflects an abnormal machine condition (machine events) or VIMS detects a control system problem (system event). Switches, sensors and other electronic control modules on the machine provide signals to VIMS. The problem signals are:

* An open switch. When a condition exceeds the trip point of the switch, the switch opens.

* A sensor signal which exceeds the limits. The main module determines the limits.

The main module analyzes the problem signals and tells the display components to activate the appropriate warning indication to notify the operator. The warning indications are:

* FLASHING of the alert indicator (approximately nine times per second).

* FLASHING of the action lamp (ON one second, OFF one second).

* SOUNDING of the action alarm (ON one second, OFF one second).

NOTE: In order to activate some warning indications more than one input is required. The main module decides when and what warning indications are activated.

Both data events and maintenance events are classified into multiple warning categories, of which three are shown to the operator. The categories are based on how severe the problem is and dictate the required response of the operator. Warning category 1 represents the least severe problem and warning category 3 represents the most severe problem. The warning categories are identified for the operator according to the combination of warning indications that are active. See the Warning Operation chart. If multiple events are present, they will be scrolled on the message area in three second intervals. When a category 3 event is active, category 1 and 2 events cannot be scrolled.

Some warnings are automatically raised to the next category depending on the length of time the problem is present. For example, on off-highway trucks: the warning category 2 for transmission lube temperature becomes warning category 3 after 150 seconds.

When a category 1 or category 2 event occurs, the operator may acknowledge that they have been notified of the event. The operator acknowledges these events by pressing the OK key on the keypad. The time and number of acknowledgements for each event is stored in the event list. After an event is acknowledged, the warning indications may disappear for a specified time period. After the time period elapses, if the event is still active, the warning indications will reappear. These warnings may be acknowledged again.

The 2-S Category is a conventional Category 2 with a continuous action alarm meaning a "severe" Category 2. A Category 2 means the operator is to change machine operation to correct the warning condition. A Category 2-S means the operator is to IMMEDIATELY change machine operation for a condition such as engine overspeed.

NOTE: Most category 3 events cannot be acknowledged by the operator.