ROD 9R3979 - Caterpillar

Illustration 1 g03086021
This diagnostic code is recorded when the 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 machine harness has failed.
The ECM has failed. This is unlikely.Test Step 1. CHECK THE CHARGING SYSTEM.
Turn the disconnect switch and the key start switch to the ON position.
Enter the diagnostic menu on the monitor. Observe the status of the diagnostic code.Expected Result:The diagnostic code is NO longer active.Results:
YES - The diagnostic code is NO longer active.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.
Start the engine.
View the status of the diagnostic code.Expected Result:The diagnostic code is NO longer active.Results:
YES - The diagnostic code is NO longer active.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 recurrenceSTOP
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 informationSTOPTest Step 3. CHECK THE BATTERY VOLTAGE.
The engine should not be running.
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: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the cause of the diagnostic code is NOT found, replace the ECM. See 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 systemSTOP