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 3 means that the ECU has determined that the voltage of the solenoid circuit is above normal.

The possible causes of the diagnostic trouble code are listed:

• The solenoid has failed.

• The energize circuit of the solenoid is shorted to the +battery circuit.

• 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 3 is active before performing this procedure.

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

Test Step 1. CHECK THE ENERGIZE CIRCUIT OF THE SOLENOID FOR A SHORT TO THE +BATTERY CIRCUIT.

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

2. Disconnect the machine harness connectors from the solenoid and the ECU.

3. At the machine harness connector for the ECU, measure the resistance from contact J1-65 to all contacts that are used in the machine harness connectors for the ECU.

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 2.

• NOT OK - Each resistance measurement is not greater than 5000 ohms. There is a short in the machine harness. The short is between J1-65 and the circuit that has a low resistance measurement.

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

  STOP

Test Step 2. CHECK THE OPERATION OF THE ECU.

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

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

2. Reconnect the machine harness J1 and J2 connectors to the ECU.

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

4. Observe the status of the active diagnostic code.

Expected Result:

The FMI 3 changes to an FMI 5 after the wire is disconnected.

Results:

• YES - The FMI 3 changes to a FMI 5 after the wire is disconnected. The ECU has responded correctly to the condition of an open circuit. Reinstall the disconnected wire to the correct space in the ECU before proceeding to the next Test Step. Proceed to Test Step 3.

• NO - The FMI 3 remains active. The status of the active diagnostic code did not change when the wire was disconnected from the ECU.

  Repair: The ECU has not responded correctly to the condition of an open 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 3. CHECK IF THE DIAGNOSTIC CODE IS STILL ACTIVE.

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 in order to make sure that the connectors are fully seated. Also, make sure 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 machine.

6. Determine if the diagnostic code is active.

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 or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.STOP