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 electronic control module (ECM) reads the electrical system voltage as being below normal.

The possible causes of this diagnostic code are listed:

• A charging system component has failed.

• The machine harness has failed.

• The ECM has failed. This event is unlikely.

Test Step 1. CHECK THE BATTERY VOLTAGE.

Use a calibrated digital multimeter for the measurements in this test procedure.

1. Start the engine and run the engine at high idle for several minutes.

2. Measure the voltage of the battery at the battery posts.

Expected Result:

The battery voltage should be greater than 18 VDC.

Results:

• OK - The battery voltage is greater than 18 VDC. The battery voltage is correct. Proceed to Test Step 2.

• NOT OK - The battery voltage is not greater than 18 VDC.

  Repair: Check the charging system.

  STOP

Test Step 2. CHECK THE SYSTEM VOLTAGE AT THE ECM.

1. The engine remains running at high idle.

2. Do not disconnect the machine harness from the ECM.

3. Use the digital multimeter to measure the voltage between all of the possible sources of power and all of the possible sources of ground.

Expected Result:

The voltage measurement is greater than 18 VDC.

Results:

• OK - The voltage is greater than 18 VDC. The battery voltage is correct. Proceed to Test Step 3.

• NOT OK - The voltage is not correct. The machine harness has failed.

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

  STOP

Test Step 3. CHECK IF THE DIAGNOSTIC CODE REMAINS.

1. Perform the following:

   • Visually inspect the harness connectors.

   • Clean the contacts of the harness connectors.

   • Visually inspect 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. Verify the following:

   • The connectors are fully seated.

   • The clips for each connector are 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 not active.

Results:

• OK - The diagnostic code is not active. 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. The problem does not exist at this time. Resume normal machine operation.

  STOP

• NOT OK - The diagnostic code is active. The problem has not been corrected. The ECM may have failed.

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

  STOP