950K and 962K Wheel Loaders Electrohydraulic System Caterpillar

Illustration 1	g02475852
Connections of the Cab Air Temperature Sensor

This diagnostic code is associated with the Cab Air Temperature Sensor. The FMI 04 means that the Implement ECM has determined that the voltage of the sensor signal circuit is below normal. The Relay Driver Module communicates the information for this diagnostic code via CAN Datalink.

The sensor resistance range is 33,650 ohms at −40° C (−40° F) to 18.6 ohms at 150° C (302° F).

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 Relay Driver Module has failed. This condition is unlikely.

Note: 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, that all connections are secure and that all connections are 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.

Test Step 1. CHECK THE SENSOR

1. Turn the disconnect switch and the key start switch to the ON position.

2. Ensure that the diagnostic code is active.

3. Observe the status of the diagnostic code. Disconnect the sensor from the machine harness.

Expected Result:

The CID 0779 FMI 04 diagnostic code changes to a CID 0779 FMI 03 diagnostic code when the sensor is disconnected from the machine harness.

Results:

• YES - The CID 0779 FMI 04 diagnostic code changes to a CID 0779 FMI 03 diagnostic code when the sensor is disconnected. The sensor has failed.

  Repair: The sensor is causing the problem. Replace the temperature sensor.

  STOP

• NO - Disconnecting the sensor from the machine harness did not change the status for the active diagnostic code. The CID 0779 FMI 04 diagnostic code is still active. The sensor is not causing the problem. Proceed to Test Step 2.

Test Step 2. CHECK THE SENSOR CIRCUIT FOR A SHORT

The sensor remains disconnected from the machine harness.

1. Turn the key start switch and the disconnect switch to the OFF position.

2. Disconnect the machine harness connector J1 from the Relay Driver Module.

3. At the machine harness connector for the Relay Driver Module, measure the resistance from the signal contact J1-30 (wire C552-WH(White)) to frame ground. Measure the resistance from the signal contact J1-30 (wire C552-WH(White)) to all of the contacts that are used in the machine harness connectors for the Relay Driver Module.

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 are less than 5000 ohms. There is a short in the machine harness.

  Repair: The short is between signal wire C552-WH(White) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.

  STOP

Test Step 3. CHECK THE OPERATION OF THE ECM

The key start switch and the disconnect switch remain in the OFF position. The machine harness connector for the sensor and the Relay Driver Module connector remain disconnected.

1. At the machine harness connector of the Relay Driver Module J1, use a 151-6320 Removal Tool to remove the energize wire of the solenoid C552-WH(White) and the socket at contact J1-30 from the harness connector.

2. Reconnect the machine harness connector J1 to the Relay Driver Module.

3. Turn the key start switch and the disconnect switch to the ON position.

4. Observe the status of the CID 0779 FMI 04 diagnostic code.

Expected Result:

The CID 0779 FMI 04 diagnostic code is no longer active. A CID 0779 FMI 03 diagnostic code becomes active when the wire C552-WH(White) at J1-30 is disconnected from the Relay Driver Module connector.

Results:

• YES - The CID 0779 FMI 04 diagnostic code is no longer active. A CID 0779 FMI 03 diagnostic code becomes active when the wire C552-WH(White) at J1-30 is disconnected from the Relay Driver Module connector. The Relay Driver Module has responded correctly to the open circuit condition in the sensor circuit. Most likely cause of the problem is not the Relay Driver Module. Reinstall the disconnected sensor signal wire back into the correct spot in the Relay Driver Module connector before proceeding to the next test step. Proceed to Test Step 4.

• NO - The CID 0779 FMI 04 diagnostic code remains active. The status of the active diagnostic code does not change when the sensor wire is disconnected from the Relay Driver Module.

  Repair: The Relay Driver Module has not responded correctly to the open condition in the sensor circuit. The operation of the Relay Driver Module is not correct.

  Prior to replacing a Relay Driver Module, always contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may effect repair time. If the Relay Driver Module or ECM must be replaced, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP

Test Step 4. CHECK THE STATUS OF THE DIAGNOSTIC CODE

1. Inspect the harness connectors. Clean the contacts of the harness connectors. Check the wires for damage to the insulation that can be caused by excessive heat, battery acid, or chafing.

2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit.

3. Reconnect all harness connectors. Make sure that the connectors are fully seated and locked.

4. Turn the disconnect switch and the key start switch to the ON position.

5. Operate the machine.

6. Check the status of the CID 0779 FMI 04 diagnostic code.

Expected Result:

The CID 0779 FMI 04 diagnostic code is active.

Results:

• YES - The CID 0779 FMI 04 diagnostic code is active. The problem has not been corrected.

  Repair: If available, perform a Wiggle Test on the sensor circuit of the machine wiring harness with the Caterpillar Electronic Technician (CAT ET). The Wiggle Test can be used to detect the following in the machine wiring harness:

  If the cause of the problem is not found, the Relay Driver Module may have failed.

  Prior to replacing a Relay Driver Module, always contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may effect repair time. If the cause of the diagnostic code is not found, replace the Relay Driver Module or ECM that has activated the diagnostic code. See the Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP

• NO - The CID 0779 FMI 04 diagnostic code is not active. The problem does not exist at this time.

  Repair: The initial diagnostic code was probably caused by a poor electrical connection at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.

  STOP