793F CMD Off-Highway Truck (Command for Hauling) Power Train Electronic Control System Caterpillar

Illustration 1	g02732776
Electrical system voltage connections

This diagnostic code is recorded when the ECM reads the electrical system voltage as being above normal.

The possible causes of this diagnostic code are listed:

• A charging system component has failed.

• The wiring of the machine harness has failed.

• The ECM has failed. This is unlikely.

Test Step 1. CHECK THE STATUS OF THE DIAGNOSTIC CODE.

1. Start the engine.

2. Clear the diagnostic code.

3. Operate the machine.

4. View the status of the diagnostic code.

Expected Result:

The diagnostic code is not active.

Results:

• OK - The diagnostic code is not active. Watch for a recurrence.

  STOP

• NOT OK - The diagnostic code is active. The charging system is charging at an excessive voltage.

  Repair: Check the charging system.

  STOP

Test Step 2. CHECK THE CHARGING SYSTEM COMPONENTS

Reference: Refer to Troubleshooting, REHS0354 manual for detailed instructions on troubleshooting the charging system components.

Expected Result:

The charging system is operating normally.

Results:

• OK - The charging system is operating normally. Proceed to Test Step 3.

• NOT OK - The charging system is not operating normally.

  Repair: Repair the charging system in accordance with Troubleshooting, REHS0354.

  STOP

Test Step 3. CHECK THE INTEGRITY OF THE CONNECTORS THAT ARE IN THE CHARGING SYSTEM

1. Inspect the harness connectors. Clean the contacts of the harness connectors. Check the wires for damage to the insulation that is caused by excessive heat, corrosion, 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 make sure that the clips for each connector are completely fastened.

4. Use the Caterpillar Electronic Technician (Cat ET) service tool in order to perform a wiggle test on the machine wiring harness. The wiggle test can detect intermittent shorts or opens in the machine wiring harness.

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

6. Operate the machine.

7. Determine if the CID 0168 FMI 03 diagnostic code is active.

Expected Result:

The CID 0168 FMI 03 diagnostic code is active.

Results:

• YES - The CID 0168 FMI 03 diagnostic code is active. The problem has not been corrected. Proceed to Test Step 4.

• NO - The CID 0168 FMI 03 diagnostic code 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 or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.

  STOP

Test Step 4. CHECK THE CHARGING SYSTEM FOR A SHORT IN THE HARNESS.

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

2. Disconnect the machine harness connectors from the alternator and the ECM.

3. Measure the resistance between the terminal of the "R" wire and all the contacts of the harness that are used for the charging system.

4. Measure the resistance between the terminal of the "F" wire and all the contacts of the harness that are used for the charging system.

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• OK - The resistance is greater than 5000 ohms. The circuit is correct. The ECM may have failed.

  Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Contact the technical communicator of your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM must be replaced, see the Testing and Adjusting, "Electronic Control Module (ECM) - Replace" Section of this manual.

  STOP

• NOT OK - The resistance is less than 5 ohms. The charging circuit is shorted to another circuit in the harness.

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

  STOP