MH3022, MH3024 and MH3026 Material Handlers Hydraulic System Caterpillar

Electronic Control System

Illustration 1	g03744623
Diagram of the machine control electronic communication system (1) Machine ECM (2) Implement ECM (3) Travel pedal (4) Engine ECM (5) CAN A data link (6) Machine monitor (7) Machine security system (8) CAN B data link (9) Operator control panel (10) Product link (11) Service connector (12) Communication adapter III (13) Electronic Technician (ET)

The following will deal primarily with the main control valve system and components that are controlled by the "Machine ECM" and the attachment "Implement ECM".

When using this manual for the troubleshooting of the electrical system circuits, the complete electrical system schematic for your machine should also be used. Quick reference electrical connection diagrams are included throughout this manual. However, these diagrams do not show the machine wiring harness connections that are part of the circuit. The complete electrical system schematic illustrate all machine wiring harness connectors and the locations on the machine.

Illustration 2	g03744628
Electronic control modules are located to left rear side of the machine (1) Machine ECM (2) Implement ECM

Machine ECM

The machine ECM is the control module that will use the programmed control logic to manage the operation of most of the machine functions. The machine ECM will use the data from the various input devices to determine the appropriate output response to operator commands.

The machine ECM determines all of the appropriate output commands and communicates this information to the Implement ECM on the SAE J1939 (CAN) data link.

The machine ECM will activate outputs in order to energize or de-energize solenoids that will control the installed machine functions.

Except for the operation of the engine, the machine ECM will control the major machine functions on the machine. These functions include the following:

• Electronic shifting of the transmission and travel functions

• Implement control

• Left and the right electronic joystick operation

• Oscillating axle operation

In addition, the machine ECM will control the following attachment functions when installed on the machine:

• Auxiliary hydraulics

• Medium pressure hydraulics

• Overload warning

• Quick coupler

• Travel alarm

• Travel lock

Illustration 3	g03744624
Machine ECM connectors (1) J1 connector (2) J2 connector

Pin Locations for Machine ECM

Illustration 4	g03744622
Machine ECM connector (70-pin)

Inputs

The inputs describe the status of the machine systems. Two types of inputs exist. The inputs can be either a switch type or a sensor type. Switches provide an open, a ground, or a + battery signal to the inputs of the controller. Sensors (frequency, PWM, or voltage) provide a changing signal to the sensor inputs of the controller.

Sensor Inputs

Most sensor input circuits have an internal ECM "pull up voltage" that is present at the ECM contacts. An above normal voltage is internally connected to the ECM input circuit through a resistor. During normal operation, the sensor signal will hold the circuit at a certain signal amplitude. However, conditions such as a loss of power to a component, a disconnection, or an open circuit allow the circuit to be pulled high. The circuit is pulled high by the ECM pull up voltage. This situation will result in an above normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 03 (voltage above normal) diagnostic code for the affected circuit.

The types of ECM input sensor circuits that have pull up voltage present are:

• Pulse Width Modulated (PWM) sensor input circuits

• Active analog (voltage) input signal circuits

• Passive analog (resistance) input signal circuits

Pulse Width Modulated (PWM) Position Sensor Operation

When powered up, the position sensors continuously send a Pulse Width Modulated (PWM) square wave signal to the ECM. Any movement on a specific axis is detected by the position sensor for that axis. The duty cycle of the PWM sensor signal changes depending on the direction and amount of movement on the axis. The duty cycle is the percentage of time that the signal is high verses the amount of time the signal is low for one cycle. The more time that the duty cycle is high, the greater the percentage of the duty cycle will be.

The percentage of duty cycle signal for a typical position sensor will be recognized as valid is 10 ± 5 to 90 ± 5 percent. These percentages occur the extreme ends of the axis movement. A typical joystick thumbwheel that is in the center or neutral position would result in a duty cycle signal of approximately 50 ± 5 percent. For a foot pedal that is not depressed, a typical duty cycle signal would be 10 ± 5 percent. The duty cycle would be 90 ± 5 percent when the pedal is depressed.

The position sensors are calibrated by the ECM to relate a specific duty cycle signal to a specific axis position for the device being monitored.

The ECM will convert the duty cycle from the position sensor to a calibrated duty cycle signal. The ECM uses this signal and a software "map" to determine the appropriate output signal that will be applied to an output device.

Note: None of the PWM sensors on the M300F Series machines require manual calibration. The machine ECM will perform an automatic calibration procedure at ECM power up.

The main control valve system contains the following sensors:

• Load sense pressure sensor

• Main pump pressure sensor

Outputs

The ECM responds to inputs by sending electrical signals to the outputs. The outputs can create an action or the outputs can provide information to the operator or service technician.

On/Off Solenoids

For control of on/off type solenoids and relays, the ECM will either turn ON or turn OFF the output for a component. The output command is based on the signals from the input devices that are involved in the system. The ECM will not vary the amplitude of the output, the circuit is either energized (on) or the circuit is de-energized (off). When the on/off output circuit is energized, most often system power will be used to energize the circuit and the output component.

Illustration 5	g01158530

Note: The values in Table 3 are for bench testing only. Values may not represent parameters for machine systems specifications.

The heavy lift on/off solenoid is utilized by the main control valve system.

Soft Switch Panel

Illustration 6	g03784851
Soft switch panel (1) Overload warning enable control button

Pin Locations for Soft Panel Switch

Heavy Lift Function

When the ECM energizes the heavy lift solenoid, the hydraulic pressure output from the main hydraulic pump will be increased by 7 percent.

For the ECM to enable the heavy lift function, all of the following conditions must be correct for the duration that the solenoid is energized.

• The travel pedal position sensor is indicating the travel pedal is not depressed.

• The service brake pedal must be locked or the parking brake must be ON.

When the machine conditions are correct and the heavy lift enable button is pressed, the ECM will energize the heavy lift Solenoid for 60 seconds. The heavy lift enable button is located on the right joystick. Pressing the button again during the 60 second cycle time will not extend the ON time for the solenoid. Once the 60 second cycle is complete, the button can be pressed again and the ECM will energize the solenoid for another 60 seconds period.

Note: If the heavy lift cycle is disabled due to a change in the machine conditions, the machine will continue to hold the load. However, the ECM will de-energize the solenoid and the main pump boost will be turned OFF.

If the machine control has activated a diagnostic code for the travel pedal position sensor circuit or the service brake pedal limit switch, the heavy lift function will not be enabled.