The Digital Sensor Supply provides power to all digital sensors. The Electronic Control Module (ECM) supplies 8.0 ± 0.4 VDC from the ECM connector J1/P1 to each digital sensor connector pin "A". The digital sensor return is used as the return line for the digital sensors, engine speed/timing sensors, and the switch inputs to the ECM. The digital return line is from the ECM connector J1/P1 to each digital sensor connector pin "B". The digital sensor supply is output short circuit protected. A short circuit to the battery will not damage the circuit inside the ECM. The digital sensors are NOT protected from overvoltage.
The following list contains a description of the Digital Sensors that are found on the engine.
Right Exhaust Temperature Sensor - The ECM uses the signal from the sensor to monitor right exhaust temperature. The sensor is mounted in the right exhaust manifold before the turbocharger. The sensor output is a constant frequency signal with a pulse width that varies with the exhaust temperature. The output signal is referred to as a Duty Cycle or as a Pulse Width Modulated signal. The output signal is expressed as a percentage between 0 and 100 percent. The Cat ET will display the exhaust temperature as a value between 49 °C to 850 °C (120 °F to 1562 °F). If the actual temperature is between -40 °C to 49 °C (-40 °F to 120 °F), the display will read 30 °C (86 °F). If the temperature is above 851 °C (1564 °F), the display will read 851 °C (1564 °F).
Left Exhaust Temperature Sensor - The ECM uses the signal from the sensor to monitor left exhaust temperature. The sensor is mounted in the left exhaust manifold before the turbocharger. The sensor output is a constant frequency signal with a pulse width that varies with the exhaust temperature. The output signal is referred to as a Duty Cycle or as a Pulse Width Modulated signal. The output signal is expressed as a percentage between 0 and 100 percent. The Caterpillar Electronic Technician (ET) will display the exhaust temperature as a value between 49 °C to 850 °C (120 °F to 1562 °F). If the actual temperature is between -40 °C to 49 °C (-40 °F to 120 °F), the display will read 30 °C (86 °F). If the temperature is above 851 °C (1564 °F), the display will read 851 °C (1564 °F).
Throttle Position Sensor - The Throttle Position Sensor (TPS) provides a throttle position signal to the engine's Electronic Control Module (ECM). The Pedal Mounted TPS is attached directly to the assembly. The Pedal Mounted TPS can not be adjusted. The Throttle Position Sensor provides a pulse width modulated signal. The signal varies with the throttle position. The signal is expressed as a percentage between 0 and 100 percent. The pedal mounted throttle position sensor will produce a minimum duty cycle when the pedal is released. The pedal mounted throttle position sensor will produce a maximum duty cycle when the pedal is fully depressed.
Engine Fan Speed Sensor - The engine fan speed sensor receives a supply voltage of 8 ± 0.4 VDC from the ECM. The sensor outputs a frequency that is directly proportional to fan speed. The sensor generates a signal pulse for each revolution of the fan. The output frequency varies between 0.83 Hz to 30 Hz over a speed range between 50 rpm and 1800 rpm.
Note: Parameters may affect the behavior of the engine. Users can use the Caterpillar Electronic Technician (ET) in order to monitor parameter settings: warnings, derates, shutdown override setpoints and delay times. The behavior of the ECM may vary from the description that is given in this System Operation section. Refer to the diagnostic procedure Troubleshooting, "System Configuration Parameters" in order to determine if there are any parameters that are affecting engine operation.
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| Illustration 1 | g00920298 |
Test Step 1. Check for Connector Damage.
- Turn the battery disconnect switch to the OFF position.
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
- Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).
- Check the customer connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring should be free of corrosion, of abrasion or of pinch points.
Results:
- OK - The connectors and wiring are okay. Proceed to test step 2.
- Not OK - The connectors and/or wiring are not okay.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 2. Check for a Short Circuit in the Wiring Harness.
- Disconnect ECM connector J1/P1 and all of the digital sensors.
- Measure the resistance between the digital supply P1-35 (A700-OR) and the digital return P1-29 (998-BR) on connector P1.
- Measure the resistance between the digital supply P1-35 (A700-OR) and engine ground.
- Measure the resistance between the digital return P1-29 (998-BR) and engine ground.
Expected Result:
The resistance should be greater than 20,000 Ohms for each measurement.
Results:
- OK - The resistance is greater than 20,000 Ohms. Proceed to test step 3.
- Not OK - The resistance is less than 20,000 Ohms.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 3. Check the Digital Supply Voltage at the ECM.
- Remove the wire A700-OR from the harness side of the ECM connector P1-35. Install a wire jumper into the socket for P1-35.
- Remove the wire 998-BR from the harness side of the ECM connector P1-29. Install a wire jumper into the socket for P1-29.
Note: If the sensors are disconnected from the harness, an open circuit diagnostic code will be generated for all of the sensors. Troubleshoot the original code. Delete the logged diagnostic codes when you are finished.
- Turn the battery disconnect switch to the ON position.
- Turn the keyswitch to the ON position. The engine should be off.
- Measure the voltage between P1-29 and P1-35 at the ECM connector P1.
- Turn the keyswitch to the OFF position.
- Replace all wires and reconnect ECM connector J1/P1.
Expected Result:
The supply voltage should be 8.0 ± 0.4 VDC.
Results:
- OK - The supply voltage is 8.0 ± 0.4 VDC. The digital sensor supply is producing the correct voltage. Proceed to test step 4.
- Not OK - The supply voltage is not 8.0 ± 0.4 VDC. The digital sensor is not producing the correct voltage.
Repair: Perform the diagnostic functional test Troubleshooting, "Electrical Power Supply".
Stop.
Test Step 4. Check the Digital Sensor Supply Voltage at the Sensor Connector.
- Turn the keyswitch to the ON position. The engine should be off.
- Measure the digital sensor supply voltage between the digital supply terminal-A (A700-OR) and the digital return terminal-B (998-BR) of all the digital sensors.
Note: If the sensor is disconnected from the harness, an open circuit diagnostic code will be generated for that sensor. Troubleshoot the original code. Delete the logged diagnostic codes when you are finished.
- Turn the keyswitch to the OFF position.
Expected Result:
The supply voltage should be 8.0 ± 0.4 VDC.
Results:
- OK - The supply voltage is 8.0 ± 0.4 VDC at all of the digital sensor connectors. Proceed to test step 5.
- Not OK - The supply voltage is not 8.0 ± 0.4 VDC. There is an open circuit in the harness or connectors.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 5. Check the Digital Sensors for Short Circuits.
- Turn the keyswitch to the ON position. The engine should be off.
Note: If the sensor is disconnected from the harness, an open circuit diagnostic code will be generated for that sensor. Troubleshoot the original code. Delete the logged diagnostic codes when you are finished.
- Connect one digital sensor at a time.
- Measure the voltage between the digital sensor supply P1-35 and the digital sensor return P1-29 at ECM connector J1/P1. Repeat these steps with all of the digital sensors.
- Turn the keyswitch to the OFF position.
Expected Result:
The supply voltage should be 8.0 ± 0.4 VDC.
Results:
- OK - The supply voltage is 8.0 ± 0.4 VDC. The digital sensor supply is correct. The harness and sensors are okay.
Repair: The problem is intermittent. Perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".
Stop.
- Not OK - The supply voltage is not 8.0 ± 0.4 VDC. The sensor may be internally shorted.
Repair: Temporarily install a new sensor. Ensure that the problem is no longer present. Reinstall the old sensor. If the problem returns, replace the sensor.
Stop.