System Operation Description:
The digital sensors receive a regulated voltage supply of 8 ± 0.4 VDC from the Electronic Control Module (ECM).
Note: Refer to Troubleshooting, “Digital Sensor Supply Circuit – Test” if the ECM has detected a problem with the digital sensor supply voltage.
The ECM performs an automatic calibration of these sensors whenever the ECM is powered and the engine is off for at least five seconds.
Verify that the auxiliary temperature sensor has been programmed to “Enabled” on the configuration screen of the Caterpillar Electronic Technician (ET). If the auxiliary temperature is not programmed, Cat ET will display “Unavailable” on the status screen.
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| Illustration 1 | g01080717 |
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Schematic for auxiliary temperature sensor |
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Test Step 1. Inspect Electrical Connectors and Wiring
- Place the engine control in the OFF/RESET mode.
- Thoroughly inspect the J1/P1 ECM connector, the customer connector, and the sensor connector that is in the circuit. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector, in the customer connector, and in the sensor connector that is associated with the auxiliary temperature sensor circuit.
- Check the ECM Connector (allen head screw) for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.
- Check the customer connector (allen head screw) for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK – The connectors and wiring are OK. Proceed to Test Step 2.
- Not OK – There is a problem in the connectors and/or wiring.
Repair: Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.Verify that the repair eliminates the problem.
STOP
Test Step 2. Check the Sensor Supply Voltage at the Sensor Connector
- Disconnect the suspect sensor.
- Place the engine control in the ON mode.
- Use a multimeter to measure the voltage across terminal A (+8V Digital) and terminal B (Digital Return) at the harness side of the connector for the auxiliary temperature sensor.
- Place the engine control in the OFF/RESET mode.
Expected Result:
The digital sensor supply voltage is 8.0 ± 0.4 VDC.
Results:
- OK – The supply voltage is reaching the sensor. Proceed to Test Step 3.
- Not OK – The digital sensor supply voltage is not reaching the sensor.
Repair: Refer to Troubleshooting, “Digital Sensor Supply Circuit – Test” for the appropriate troubleshooting procedure.
STOP
Test Step 3. Check for Opens in the Wiring
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| Illustration 2 | g00806454 |
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P1/J1 schematic |
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| Illustration 3 | g00806473 |
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P61/J61 Schematic |
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- Disconnect the following connectors.
- P142/J142 (auxiliary temperature sensor)
- J1/P1 (ECM connector)
- J61/P61 (customer connector)
- Measure the resistance between the following terminals.
- P1-4 to J61-8
- P1-5 to J61-9
- P1-68 to J61-11
- P61-8 to P142-A
- P61-9 to P142-B
- P61-11 to P142-C
Expected Result:
The resistance through the signal wire is less than 5 Ohms.
Results:
- OK – The resistance through the signal wire is less than 5 Ohms. Proceed to Test Step 4.
- Not OK – The resistance through the signal wire is more than 5 Ohms. There is an open circuit or excessive resistance in the signal circuit of the harness.
Repair: Repair the circuit.Verify that the repair eliminates the problem.
STOP
Test Step 4. Check for Shorts in the Wiring
- Reconnect the customer connector J61/P61.
- Check the resistance between the following terminals of ECM connector P1 and every pin in ECM connector P1. Check the resistance between the following terminals of ECM connector P1 and every pin on ECM connector P1.
- P1-4
- P1-5
- P1-68
Expected Result:
The resistance is greater than 20,000 Ohms for each measurement.
Results:
- OK – The resistance is greater than 20,000 Ohms for each measurement. The signal wire is good. Proceed to Test Step 5.
- Not OK – The resistance is less than 20,000 Ohms for each measurement. The signal wire is shorted.
Repair: Repair the circuit.Verify that the repair eliminates the problem.
STOP
Test Step 5. Install a New Sensor
- Temporarily install a new sensor.
- Reconnect any connectors that have been disconnected in the troubleshooting process.
- Place the engine control in the ON mode.
- Check for diagnostic codes on Cat ET.
- Place the engine control in the OFF/RESET mode.
Expected Result:
There are no active diagnostic codes for the suspect sensor.
Results:
- OK – Installing a new sensor fixed the problem.
Repair: Permanently install the new sensor.Verify that the repair eliminates the problem.
STOP
- Not OK – Installing the new sensor did not fix the problem. The signal wire is good and the sensor is receiving the proper supply voltage.
Repair: Verify your results before replacing the ECM. Refer to Troubleshooting, “Replacing the ECM” before you replace the ECM.Verify that the repair eliminates the problem.
STOP
