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| Illustration 1 | g01757516 |
Schematic of the Cab Air Temperature Sensor | |
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| Illustration 2 | g01895214 |
Location of the cab air temperature sensor | |
This diagnostic code is associated with the Cab Air Temperature sensor. This diagnostic code is recorded when the ECM reads the signal from the sensor (wire C552-WH) as being shorted to the +Battery. The signal (wire C552-WH) connects to contact J1-22 of the ECM.
Possible causes of the diagnostic code is listed:
- The return circuit is open.
- The signal circuit is open or the sensor is disconnected.
- The signal circuit is shorted to the +Battery.
- The sensor has failed.
- The ECM has failed. This is unlikely.
Before performing this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure and in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.
System Response:
A level 1 warning will be generated.
Note: Ensure that CID 0779 FMI 03 is active. This procedure can cause new diagnostic codes to be recorded. Ignore these created diagnostic codes. When the procedure is completed, clear the created diagnostic codes.
Test Step 1. CHECK FOR AN OPEN IN THE RETURN CIRCUIT.
- Turn the key start switch and the disconnect switch to the OFF position.
- The sensor remains disconnected from the machine harness.
- Disconnect the machine harness connector J1 from the ECM.
- At the machine harness connector for the sensor, measure the resistance from contact 2 (wire J767-GY) to ground.
Expected Result:
The resistance measurement should measure less than 5 ohms.
Results:
- OK - The resistance measurement is less than 5 ohms. The harness is correct.
Repair: The ECM may have failed. Recheck the status of the diagnostic code. If the diagnostic code remains present, exit this procedure and perform this procedure again. If the cause of the problem is not found, contact the Technical Communicator for your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, see Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
STOP
- NOT OK - The resistance that is measured is not correct.
Repair: There is an open in the machine harness. The open is in the return circuit with the high resistance measurement. Repair the harness or replace the harness.
STOP
Test Step 2. CHECK FOR AN OPEN IN THE SIGNAL CIRCUIT.
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the J1 and J2 machine harness connector from the ECM.
- At the machine harness connector for the sensor, install a jumper wire from contact 1 (wire C552-WH) to contact 2 (wire J767-GY).
- At the machine harness connector J1, measure the resistance from contact J1-22 (wire C552-WH) to Frame Ground.
Expected Result:
The resistance measurement is less than 5 ohms.
Results:
- OK - The resistance measures less than 5 ohms. Proceed to 3.
- NOT OK - The resistance measurement is greater than 5 ohms.
Repair: There is an open in the signal circuit. Repair the harness or replace the harness.
STOP
Test Step 3. CHECK THE SIGNAL CIRCUIT FOR A SHORT.
- The disconnect switch and the key start switch remain in the OFF position.
- The machine harness connectors J1 and J2 remain disconnected.
- Remove the jumper wire from contact 1 (wire C552-WH) to contact 2 (wire J767-GY).
- At the J1 and J2 machine harness connectors for the ECM, measure the resistance for the signal contact of the sensor J1-22 (wire C552-WH) to all other J1 and J2 contacts.
Expected Result:
Each resistance measurement is greater than 5000 ohms.
Results:
- OK - Each resistance measurement is greater than 5000 ohms.
Repair: The sensor has failed. Replace the sensor and verify that the new sensor corrected the problem. If the problem persists, exit this procedure and perform this procedure again. If the cause of the problem is not found, contact the Technical Communicator for your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, see Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
STOP
- NOT OK - Any resistance measures less than 5000 ohms.
Repair: There is a short in the machine harness. The short is between the signal circuit and the circuit with the low resistance measurement. Repair the harness or replace the harness.
STOP