MXS, ; RKS and ; NXS Model Views
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| Illustration 1 | g01102476 |
Typical example Left side view of engine (1) Secondary engine speed/timing sensor (2) Intake manifold pressure sensor (Boost) (3) Front valve cover connector (4) Intake manifold air temperature sensor (5) Rear valve cover connector (6) Primary engine speed/timing sensor (7) Timing calibration port (8) Fuel temperature sensor (9) Atmospheric pressure sensor (10) Engine oil pressure sensor (11) Engine Control Module (ECM) (12) J2/P2 ECM connector (13) J1 ECM connector | |
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| Illustration 2 | g01102478 |
Right side of engine (14) Sensor for the intake valve actuation pressure (15) Solenoid for the intake valve actuation pressure (16) Coolant temperature sensor (17) Diverter valve for the engine coolant | |
BXS Model Views
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| Illustration 3 | g01102758 |
Left side of engine (1) Secondary engine speed/timing sensor (2) Intake manifold pressure sensor (Boost) (3) Front valve cover connector (4) Intake manifold air temperature sensor (5) Rear valve cover connector (6) Primary engine speed/timing sensor (7) Timing calibration port (8) Fuel temperature sensor (9) Atmospheric pressure sensor (10) Engine oil pressure sensor (11) Engine Control Module (ECM) (12) J2/P2 ECM connector (13) J1 ECM connector | |
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| Illustration 4 | g01102764 |
Right side of engine (14) Sensor for the intake valve actuation pressure (15) Solenoid for the intake valve actuation pressure (16) Coolant temperature sensor (17) Diverter valve for the engine coolant | |
Engine Monitoring
The electronic control system includes engine monitoring. The system monitors engine oil pressure, coolant temperature and coolant level. All truck engines are shipped from the factory with the following sensors: engine oil pressure sensor and coolant temperature sensor. The Original Equipment Manufacturer (OEM) is responsible for providing and installing the coolant level sensor. The coolant level sensor is the only sensor that can be individually selected for engine monitoring. The software for the Engine Control Module (ECM) contains a customer programmable parameter that enables the coolant level sensor. The default factory setting is "NO". The ECM customer programmable parameters have four levels that are for engine monitoring:
- Warning (factory default)
- Engine derate
- Engine shutdown
Warning Mode
Warning mode uses the following sensors: engine oil pressure, coolant temperature and optional coolant level sensor. When a diagnostic code is active, the check engine lamp will flash and the warning lamp will come on.
Engine Derate and Engine Shutdown
The engine derate and the engine shutdown allows the ECM to alter engine performance in order to avoid damage to the engine. The engine should return to normal conditions once the problem is corrected. When the engine is derated, the check engine lamp and the warning lamp will flash. For the operating conditions that cause these modes, refer to the appropriate section for the sensor.
Electronic Control System Operation
The fuel delivery and injection timing are electronically controlled. In comparison to engines that are controlled mechanically, the electronic control system provides increased control of timing and increased control to the fuel to the air ratio. Injection timing is achieved by precise control of injector firing time, and engine power is controlled by adjusting the firing duration. The ECM energizes the fuel injection solenoid in order to start the injection of fuel. The ECM will de-energize the fuel injection solenoid in order to stop the injection of fuel. Refer to the Systems Operation, "Fuel System" for a complete explanation of the fuel injection process.
The engine uses the following types of electronic components: input, control and output.
An input component is one that sends an electrical signal to the ECM. The signal that is sent varies in either voltage or in frequency when there is a change in some specific system of the vehicle. An example would be the engine speed/timing sensors or the coolant temperature sensor. The ECM sees the input sensor signal as information about the condition, environment, or operation of the vehicle.
An electronic control system component receives the input signals. Electronic circuits that are inside the ECM evaluate the signals. The ECM then supplies electrical energy to the output components of the system, which are in response to predetermined combinations of input signal values.
An output component is one that is operated by the ECM. An output component receives electrical energy from the ECM. The electrical energy is used to perform one of the following functions:
- Perform work. An example would be moving a solenoid plunger. An output component takes an active part in regulating or operating the vehicle.
- An output component can give information or a warning. An example would be a light or an alarm to the operator of the vehicle or other person.
Output components provide the ability to electronically control the engine operation in order to improve the following items: performance, fuel consumption rate and reduced emissions levels. A brief description of the sensors that are used in the electronic control system follows:
Atmospheric Pressure Sensor
The atmospheric pressure sensor is an absolute pressure sensor that measures crankcase pressure. Both the boost pressure and the oil pressure are communicated to the service tools and over the data link. The two pressures are calculated by subtracting the reading for the atmospheric pressure sensor. The atmospheric pressure sensor measures pressure from 0 to 116 kPa (0 to 17 psi). The atmospheric pressure sensor is supplied with + 5 VDC by the ECM.
Intake manifold pressure sensor (Boost)
The intake manifold pressure sensor is an absolute pressure sensor that measures inlet manifold pressure. The difference between the measurement of the inlet manifold pressure and the pressure that is measured by the atmospheric pressure sensor is called the boost pressure. The information is communicated to Caterpillar Electronic Technician (ET) and over the data link. The intake manifold pressure sensor measures pressures from 20 to 550 kPa (3 to 80 psi). The intake manifold pressure sensor is supplied with + 5 VDC by the ECM.
Coolant Level Sensor
The coolant level sensor is installed by the vehicle OEM. The coolant level sensor is an optional sensor. The coolant level sensor is selected through the ECM customer programmable parameter. The ECM customer programmable parameters can be protected by customer passwords.
Coolant Temperature Sensor
The engine coolant temperature is measured by an electronic sensor that is mounted on the water temperature regulator housing. The coolant temperature signal is used to modify the amount of the fuel that is delivered to the engine and the engine timing for improvement during cold starts and white smoke cleanup. The ECM supplies the coolant temperature sensor with 5.0 ± 0.5 VDC. The sensor output voltage is + 0.5 to + 4.5 VDC. The sensor output voltage depends on the engine coolant temperature. Coolant temperature is used to indicate the cold mode operation and coolant temperature is used for engine monitoring.
Coolant Temperature Engine Monitoring Operation
The check engine lamp will flash if engine monitoring is programmed to derate the engine. The check engine lamp will flash if engine monitoring is programmed to shut down the engine. The warning lamp will then flash when the associated diagnostic code is active. When the warning lamp flashes, the engine is in derate mode.
Fuel Temperature Sensor
The fuel temperature is monitored in order to adjust the calculations for the fuel rate. The temperature of the fuel is also monitored in order to correct the power of the engine. The power of the engine is altered in order to provide constant power when fuel temperatures exceed 30 °C (86 °F). The maximum correction of the power occurs when the fuel temperature reaches 70 °C (158 °F). Fuel temperature that exceeds 90 °C (194 °F) for ten minutes causes a diagnostic code to be logged.
Sensor for the Intake Valve Actuation Pressure
The sensor for the intake valve actuation pressure measures the oil pressure in the external oil rail that is located on the valve cover base. The oil pressure is communicated over the data link and the oil pressure can be displayed by Cat ET.
Engine Oil Pressure Sensor
The engine oil pressure sensor is an absolute pressure sensor that measures engine oil pressure in the oil gallery. The engine oil pressure is communicated over the data link and the engine oil pressure can be displayed by Cat ET. The ECM uses the sensor input only if the parameter for engine monitoring is programmed to Warning, Derate, or Shutdown. The engine oil pressure sensor measures pressure from 0 to 1135 kPa (0 to 165 psi). The sensor is supplied by the ECM with + 5 VDC.
Retarder Enable for the Compression Brake
If the engine is equipped with a compression brake, the operation of the compression brake is provided through the retarder enable output. The retarder enable status is determined by the ECM. In order to determine the retarder enable status, the following items are monitored by the ECM: dash switch for the compression brake, clutch switch, accelerator pedal position, cruise control switch and engine speed (rpm). Operation of the compression brake will be restricted under improper engine operating conditions. The following conditions must be met in order to enable the compression brake:
- The engine speed (rpm) is above 1000 rpm.
- The accelerator pedal not pressed.
- The clutch pedal is not depressed.
- The cruise control switch is "OFF".
- The switch for the compression brake is energized.
Primary Engine Speed/Timing Sensor and Secondary Engine Speed/Timing Sensor
This engine uses two engine speed/timing sensors. The primary engine speed/timing sensor senses the position of the crankshaft gear. The secondary engine speed/timing sensor senses the position of the camshaft gear. Both sensors detect a reference for engine speed and engine timing from a unique pattern on the gear for that sensor.
The primary engine speed/timing sensor is used for starting the engine. The secondary engine speed/timing sensor determines when the No. 1 cylinder is at the top of the compression stroke. When the timing has been established, the primary engine speed/timing sensor is used to determine the engine speed.
The engine will start and the engine will run if only one signal from the sensors is present. However, if there is no signal from either engine speed/timing sensor, the engine will stop. The loss of signal from both sensors will prevent the engine from starting.
Accelerator Pedal Position Sensor
The accelerator pedal position sensor is an electronic sensor that is connected to the accelerator pedal. The accelerator pedal position sensor sends a pulse width modulated signal to the ECM.
Vehicle Speed Sensor
The vehicle speed sensor is an electromagnetic pickup that measures vehicle speed. The sensor measures vehicle speed from the rotation of the gear teeth that are in the drive train of the vehicle.
Check Engine Lamp (Diagnostic Lamp)
The check engine lamp is sometimes referred to as the diagnostic lamp. The check engine lamp is located on the dashboard of the vehicle. The check engine lamp can be used as a diagnostic lamp in order to communicate any problems with the operation of the electronic control system.
Note: The check engine lamp and the warning lamp are different. For more information about terminology for electronic components, refer to your engine's Troubleshooting manual.
When a diagnostic fault is detected by the ECM, the check engine lamp will turn ON. When a diagnostic fault is detected by the ECM, the check engine lamp will blink at five second intervals. The check engine lamp should be ON and the check engine lamp should be flashing diagnostic code 55 whenever the keyswitch is turned ON but the engine is not running. This condition will test whether the lamp is operating correctly.
If the check engine lamp comes on and the check engine lamp stays on after the initial start-up, the system has detected a fault. The check engine lamp or service tools can be used to identify the diagnostic code.
The dash mounted cruise control switches are used to interrogate the ECM for system status. With the cruise control switches in the OFF position, move the "SET/RESUME" switch to the RESUME position. The check engine lamp will begin to flash in order to indicate a two digit diagnostic code while the "SET/RESUME" switch is held in the RESUME position. The sequence of flashes represents the system diagnostic message. The first sequence of flashes adds up to the first digit of the diagnostic code. After a one second pause, a second sequence of flashes will occur. The second sequence of flashes represent the second digit of the diagnostic code. If necessary, additional diagnostic codes will follow after a three second pause. Additional diagnostic codes will be displayed in the same manner.
The check engine lamp is also used to monitor the idle shutdown timer. The check engine lamp will start to flash at a rapid rate 90 seconds before the programmed idle time is reached. If the clutch pedal indicates a change in position or the service brake pedal indicates a change in position during the final 90 seconds, the idle shutdown timer will be disabled. The idle shutdown timer will then need to be reset.
Engine Control Module (ECM)
The ECM power supply provides electrical power to all engine mounted sensors and actuators. Reverse voltage polarity protection and resistance to vehicle power system voltage swings or surges have been designed into the ECM. The ECM also monitors all input from the sensors. The ECM also provides the correct outputs in order to ensure desired engine operation.
The ECM contains memory in order to store customer specified parameters. The ECM also identifies a factory engine rating. The memory also contains a personality module identification code in order to prevent unauthorized tampering. The memory also contains an identification code in order to prevent switching of engine ratings and other manufacturing information.
The wiring harness provides communication or signal paths to the various sensors. A boost pressure sensor, the data link connector, and the engine/vehicle connectors are examples. The ECM performs many functions. The ECM contains all of the information that regulates engine performance. The ECM contains all of the information for the emission certification. Several examples are listed: engine timing, air/fuel ratio and fuel ratio control maps.
Note: The list that follows contains a portion of the customer specified parameters: engine power rating, vehicle identification number, low gear limit, intermediate gear limit, engine speed limit, gear down protection, Top Engine Limit (TEL), Vehicle Speed Limit (VSL), controls for the vehicle's high gear, Low Cruise Control Set Limit (LCC), High Cruise Control Set Limit (HCC), retarder coast/latch and idle shutdown timer. The customer specified parameters may be secured by customer passwords. An ECM may have all of the programmed parameters or any combination of the programmed parameters. For a brief explanation of each of the customer specified parameters, refer to the Troubleshooting manual for your engine.
The ECM is programmed to run diagnostic tests in order to separate a fault to a specific circuit. Once a fault is detected, the fault can be displayed in several ways on the check engine lamp. Several examples of the displays are listed: flashing coded display (representing a diagnostic fault code) on the dash mounted check engine lamp and diagnostic codes can be read by Cat ET. The ECM will log most of the diagnostic codes that are generated during engine operation. The logged codes or the active codes can be read by Cat ET.
Relay Driver Module for the Cooling Fan
The ECM provides a disable function for the cooling fan. If the ECM output is high, the fan is off. The disable function for the cooling fan is for control of the engine's cooling fan. The on/off control is based on the following items: coolant temperature, engine brake mode and engine speed. The on/off control is also based on the air conditioning high pressure switch that is installed by the OEM. All other control of the cooling fan is the responsibility of the OEM.
In order to prevent fan clutch cycling during engine cranking due to low voltage levels, the ECM disables the fan. Because an electrical open circuit is the most likely failure mode, Caterpillar recommends a normally open relay for this circuit.