793F CMD Off-Highway Truck/Tractor Braking System Caterpillar

Illustration 1	g02748103
Schematic of the connections for the voltage of the Brake ECM

This diagnostic code is recorded when the Brake ECM reads the system voltage as being greater than 32 DCV.

The possible causes of this diagnostic code are listed below:

• A charging system component has failed.

• The wiring of the machine harness has failed.

• The Brake ECM has failed. This situation is unlikely.

System Response:

Components that are connected to the controller will not log faults.

Test Step 1. CHECK THE CHARGING SYSTEM.

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

2. Observe that the CID 0168 FMI 03 diagnostic code is active.

3. View the status of the diagnostic code.

Expected Result:

The diagnostic code is NO longer active.

Results:

• YES - The diagnostic code is NO longer active. Proceed to Test Step 2.

• NO - The diagnostic code remains active. Proceed to Test Step 3.

Test Step 2. CHECK THE CHARGING SYSTEM AGAIN.

1. Start the engine.

2. Observe that the CID 0168 FMI 03 diagnostic code is active.

3. View the status of the diagnostic code.

Expected Result:

The diagnostic code is NO longer active.

Results:

• YES - The diagnostic code is NO longer active. Watch for a recurrence

  STOP

• NO - The diagnostic code is active. The charging system is charging at an excessive voltage.

  Repair: Check the charging system. See Special Instruction, REHS0354, "Charging System Troubleshooting" for more information.

  STOP

Test Step 3. CHECK THE BATTERY VOLTAGE.

1. The engine should not be running.

2. At the battery, measure the voltage of the battery.

Expected Result:

The voltage should measure less than 32 DCV.

Results:

• YES - The voltage measures less than 32 DCV. The ECM must be recording this diagnostic code incorrectly. The ECM may have failed.

  Repair: A failure of the Brake ECM is unlikely. Exit this procedure and perform this procedure again. Prior to replacing an ECM, always contact the Technical communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP

• NO - The voltage measurement is greater than 32 DCV. The charging system is charging at an excessive voltage.

  Repair: Check the charging system.

  STOP