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 03 means that the Implement ECM has determined that the sensor circuit voltage is above normal. The Relay Driver Module communicates the information for this diagnostic code via CAN Datalink to the Implement ECM.

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:

• There is an open in the sensor circuit.

• The signal circuit is shorted to another voltage source.

• 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 CIRCUIT FOR AN OPEN CIRCUIT

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

2. Disconnect the machine harness connector from the sensor.

3. At the machine harness connector for the sensor, connect a jumper wire from the signal contact 1 (wire C552-WH(White)) to frame ground.

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

5. Observe the status of the active CID 0779 FMI 03 diagnostic code.

Expected Result:

The active CID 0779 FMI 03 diagnostic code is no longer active. A CID 0779 FMI 04 diagnostic code becomes active when the signal wire is grounded.

Results:

• YES - The active CID 0779 FMI 03 diagnostic code is no longer active. A CID 0779 FMI 04 diagnostic code has been activated after the signal wires is grounded. Proceed to Test Step 2.

• NO - The CID 0779 FMI 03 diagnostic code remains active. The status of the active diagnostic code does not change when the signal wire is grounded. There is an open or a poor connection in the signal wire.

  Repair: Check the signal circuit for an open or for a poor connection. Repair or replace the machine harness.

  STOP

Test Step 2. CHECK THE SENSOR CIRCUIT FOR A SHORT

The machine harness connector remains disconnected from the sensor. The key start switch and the disconnect switch remain in the OFF position.

1. Remove the jumper wire that was installed in the previous step.

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 all of the other 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 not correct. There is a short in the machine harness.

  Repair: The short is between the signal circuit 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 OPERATION OF THE RELAY DRIVER MODULE

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

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

2. Reconnect the machine harness connector J1 to the module.

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

4. Use a 7X-1710 Multimeter Probe to contact the Relay Driver Module pin J1-30 through the empty space in the J1 connector.

5. Observe the status of the active CID 0779 FMI 03 diagnostic code. Ground the other end of the 7X-1710 Multimeter Probe to ground location on the frame of the machine.

Expected Result:

The active CID 0779 FMI 03 diagnostic code is no longer active. A CID 0779 FMI 04 diagnostic code becomes active when the pin at J1-30 is grounded.

Results:

• YES - The CID 0779 FMI 03 diagnostic code is no longer active. A CID 0779 FMI 04 diagnostic code has been activated after the pin is grounded. The Relay Driver Module has responded correctly to the grounded circuit condition in the sensor circuit. The Relay Driver Module is most likely not causing the problem. Reconnect the signal wire and the socket in the machine harness connector J1 for the Relay Driver Module before proceeding to the next test step. Proceed to Test Step 4.

• NO - The CID 0779 FMI 03 diagnostic code remains active. The status of the active diagnostic code does not change when the pin for the sensor is grounded.

  Repair: Reconnect the signal wire and the socket in the machine harness connector J1 for the Relay Driver Module. Repeat this test step in order to verify that the Relay Driver Module is the cause of the problem.

  If the CID 0779 FMI 03 diagnostic code is still active, the Relay Driver Module has 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 Relay Driver Module or ECM require replacement, 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 03 diagnostic code.

Expected Result:

The CID 0779 FMI 03 diagnostic code is active.

Results:

• YES - The CID 0779 FMI 03 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:

  • Momentary shorts

  • Opens
  If the cause of the problem is not found, replace the temperature sensor. After the sensor is replaced, perform this test step again. If the problem is still present after replacement of the sensor, 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 03 diagnostic code 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 at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.

  STOP