CX28, CX31 and CX35 On-Highway Transmissions Power Train Electronic Control System Caterpillar

Illustration 1	g01371111
Schematic of the retarder solenoid on the CX31

Illustration 2	g01371109
Schematic of the retarder solenoid on the CX35

This diagnostic trouble code is associated with the retarder solenoid. The FMI 5 means that the ECU has determined that an open in the circuit exists.

The possible causes of this diagnostic trouble code are listed below:

• The energize circuit of the solenoid is open.

• The return circuit of the solenoid is open.

• The solenoid has failed.

• The ECU has failed. This is unlikely.

Note: The following test procedure may create other diagnostic trouble codes. Ignore these created diagnostic trouble codes and clear these diagnostic trouble codes when the original diagnostic trouble code has been corrected. Ensure that the diagnostic trouble code of SPN 744 FMI 5 is active before performing this procedure.

Note: Use a digital multimeter for the measurements in this procedure.

Test Step 1. CHECK THE SOLENOID FOR A CX31.

1. Turn the disconnect switch and the key start switch to the ON position. Do not start the engine.

2. Disconnect the solenoid with the active diagnostic code from the machine harness.

3. At the machine harness connector for the solenoid, place a jumper wire from contact 1 (wire K744-BU) to contact 2 (wire 921-WH).

4. Observe the status of the diagnostic code.

Expected Result:

The diagnostic code is active. Then, the diagnostic code changes from FMI 5 to FMI 6 as the jumper wire is installed.

Results:

• YES - The diagnostic code remains active. The jumper wire does not affect the diagnostic code. Proceed to Test Step 3.

• NO - The diagnostic is no longer active. The solenoid has failed.

  Repair: The solenoid has failed. Replace the solenoid. Verify that the new solenoid corrects the problem.

  STOP

Test Step 2. CHECK THE SOLENOID FOR A CX35.

1. Turn the disconnect switch and the key start switch to the ON position. Do not start the engine.

2. Disconnect the solenoid with the active diagnostic code from the machine harness.

3. At the machine harness connector for the solenoid, place a jumper wire from contact 1 (wire K744-BU) to contact 2 (wire 923-GY).

4. Observe the status of the diagnostic code.

Expected Result:

The diagnostic code is active. Then, the diagnostic code changes from FMI 5 to FMI 6 as the jumper wire is installed.

Results:

• YES - The diagnostic code remains active. The jumper wire does not affect the diagnostic code. Proceed to Test Step 4.

• NO - The diagnostic is no longer active. The solenoid has failed.

  Repair: The solenoid has failed. Replace the solenoid. Verify that the new solenoid corrects the problem.

  STOP

Test Step 3. CHECK THE HARNESS FOR AN OPEN FOR A CX31.

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

2. Disconnect the machine harness connector(s) from the ECU.

3. The jumper wire that was installed in the previous Test Step remains in place.

4. At the machine harness connector, measure the resistance from signal contact J1-65 to contact J1-60.

Expected Result:

The resistance is less than 5.0 ohms.

Results:

• OK - The resistance is less than 5.0 ohms. The machine harness is correct. Proceed to Test Step 5.

• NOT OK - The resistance is greater than 5000 ohms. The resistance measurement is not correct. There is an open circuit in the machine harness.

  Repair: Repair the machine harness or replace the machine harness.

  STOP

Test Step 4. CHECK THE HARNESS FOR AN OPEN FOR A CX35.

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

2. Disconnect the harness connector(s) from the ECU.

3. The jumper wire that was installed in the previous Test Step remains in place.

4. At the machine harness connector, measure the resistance from signal contact J1-65 to contact J1-55.

Expected Result:

The resistance is less than 5.0 ohms.

Results:

• OK - The resistance is less than 5.0 ohms. The machine harness is correct. Proceed to Test Step 5.

• NOT OK - The resistance is greater than 5000 ohms. The resistance measurement is not correct. There is an open circuit in the machine harness.

  Repair: Repair the machine harness or replace the machine harness.

  STOP

Test Step 5. CHECK THE OPERATION OF THE ECU.

The disconnect switch and the key start switch remain in the OFF position. The harness connector for the solenoid and the connectors for the ECU remain disconnected.

1. Remove the jumper wire that was installed in the last test step.

2. At the J2 connector for the ECU, use a wire removal tool to remove wire K744-BU from contact J1-65.

3. Reconnect the machine harness connectors to the ECU.

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

5. Use a multimeter probe that is not connected to a multimeter or a similar device to make contact with the ECU at contact J1-65 through the empty space in the J1 connector.

6. Observe the status of the diagnostic code. Ground the other end of the multimeter probe to frame ground.

Expected Result:

The FMI 5 changes to a FMI 6 when the pin is grounded at contact J1-65.

Results:

• YES - The FMI 5 changes to a FMI 6 when the pin is grounded at contact J2-4. The ECU has responded correctly to the condition of a grounded circuit. The operation of the ECU is correct. Reinstall the disconnected wire into the correct spot in the ECU before proceeding to the next Test Step.
  
  Proceed to Test Step 6.

• NO - The FMI 5 remains active. The status of the active diagnostic code does not change when contact J1-65 is grounded.

  Repair: The ECU has not responded correctly to the condition of a grounded circuit. The operation of the ECU is not correct.Prior to replacing an ECU, always contact your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECU requires replacing, refer to Testing and Adjusting, "Electronic Control Module (ECU) - Replace".

  STOP

Test Step 6. CHECK IF THE DIAGNOSTIC CODE REMAINS.

1. Inspect the harness connectors. Clean the contacts of the harness connectors and check the wires for damage to the insulation that is 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 harness connectors are fully seated and that the clips for each connector are completely fastened.

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

5. Operate the vehicle.

6. Check the status of the diagnostic code.

Expected Result:

The diagnostic code is active.

Results:

• YES - The diagnostic code is active. The diagnostic code has not been corrected.

  Repair: Check the circuit again. It is unlikely that the ECU has failed. Exit this procedure and perform this procedure again. Prior to replacing an ECU, always contact your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECU requires replacing, refer to Testing and Adjusting, "Electronic Control Module (ECU) - Replace".

  STOP

• NO - The diagnostic code is not active. The diagnostic code does not exist at this time. 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 vehicle operation.STOP