768C, 769C, 769D, 772B, 773B, 773D, 776C, 777B, 777D, 784B, 785, 785B, 789, 789B, 793, 793B and 793C Off-Highway Truck/Tractors and 771C, 771D and 775D Quarry Trucks Automatic Retarder Control (ARC) System Caterpillar

Note: Ensure that the diagnostic code is active. This diagnostic code can be active at any time when the key start switch is ON. The following procedure may cause new diagnostic codes to be recorded. When the procedure is completed, clear the diagnostic codes that were caused by the procedure. Connector contact A-A5 of the ARC is related to this diagnostic code. The ARC activates the retarder indicator lamp with a +battery signal.

1. CHECK THE SIGNAL CIRCUIT OF THE INDICATOR FOR A SHORT.

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

   2. Disconnect the machine harness from the indicator lamp.

   3. Disconnect the machine harness connectors A from the ARC.

   4. At the A machine harness connectors for the ARC, measure the resistance from the signal contact of the indicator lamp A-A5 (wire 454-GN-16) to all possible sources of positive voltage. The possible sources of positive voltage are contacts: A-A1, A-A3 and A-A4.

      Expected Result: Each resistance should be greater than 5000 ohms.

      Results:

      • OK: The resistance reading is greater than 5000 ohms. The machine harness is correct. Proceed to Step 2.

      • NO: There is a short in the machine harness. The short is between the signal contact of the indicator and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness. STOP.

2. CHECK IF THE DIAGNOSTIC CODE REMAINS.

   1. Inspect the contacts and clean the contacts of the harness connectors.

   2. Reconnect all harness connectors.

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

   4. Clear all of the inactive diagnostic codes.

   5. Operate the machine.

   6. Stop the machine. Then place the parking brake in the ON position.

   7. Observe the status of the diagnostic code. The diagnostic code is present or the diagnostic code is NOT present.

      Expected Result: The diagnostic code for the indicator is NO longer present.

      Results:

      • OK: The diagnostic code is NOT present. The diagnostic code does not exist at this time. The initial diagnostic code was probably caused by a poor electrical connection and/or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operations. STOP.

      • NO: The diagnostic code has not been corrected. It is unlikely that the ARC is faulty. Exit this procedure and perform this diagnostic code again. Recheck the status of the diagnostic code. If the cause of the diagnostic code is not found, replace the ARC. See Testing And Adjusting, "ARC - Replace".