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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. The FMI 04 means that the ECM has determined that the voltage of the circuit for the sensor is below normal.
The possible causes of this diagnostic code are listed below:
- The signal circuit for the sensor is shorted to ground.
- 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.
Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code has been corrected. Ensure that the diagnostic code of CID 0779 FMI 04 is active before performing this procedure.
Note: Use a digital multimeter for the measurements in this procedure.
System Response:
A level 1 warning will be generated.
Test Step 1. CHECK THE SENSOR
- Turn the disconnect switch and the key start switch to the ON position.
- Ensure that the diagnostic code is active.
- Disconnect the sensor from the machine harness.
- Observe the status of the diagnostic code.
Expected Result:
The CID 0779 FMI 04 remains active. The FMI has not changed and the "04" is still active.
Results:
- OK - The diagnostic code remains active. The sensor is correct. Proceed to Test Step 2.
- NOT OK - The diagnostic code changes from an FMI 04 to an FMI 03. The sensor has failed.
Repair: Replace the sensor.
STOP
Test Step 2. CHECK THE WIRING HARNESS OF THE SENSOR FOR A SHORT TO GROUND.
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the machine harness from the sensor.
- Disconnect the machine harness connector(s) from the ECM.
- At the machine harness connector for the ECM, measure the resistance from the signal contact J1-22 (wire C552-WH) of the machine harness to all possible sources of ground. Measure the resistance to all contacts of the machine harness connectors for the ECM.
Expected Result:
Each resistance measurement is greater than 5000 ohms.
Results:
- OK - Each resistance measurement is greater than 5000 ohms. The machine harness is correct. Proceed to Test Step 3.
- NOT OK - One or more resistance measurements is not correct. There is a short in the machine harness.
Repair: The short is between signal contact J1-22 (wire C552-WH) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.
STOP
Test Step 3. CHECK IF THE DIAGNOSTIC CODE REMAINS.
- Inspect the contacts of the harness connectors and clean the contacts.
- Reconnect all harness connectors.
- Turn the disconnect switch and the key start switch to the ON position.
- Operate the machine.
- Check the status of the CID 0779 FMI 04.
Expected Result:
The CID 0779 FMI 04 is active.
Results:
- YES - The CID 0779 FMI 04 is active. The diagnostic code has not been corrected. The ECM may have failed.
Repair: 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
- NO - The CID 0779 FMI 04 is not active. The diagnostic code does not exist at this time.
Repair: The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.
STOP