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

A failure is recorded when the ARC does not receive the expected information. For example, engine speed or actual gear information is not received from other electronic control modules through the CAT data link. This failure can result in the display of abnormal values on readouts that are dependent on the CAT data link information. The possible causes are listed here:

• Poor electrical connection at a machine harness connector

• CAT data link circuit in the machine harness is shorted to ground.

• CAT data link circuit in the machine harness is shorted to the +battery.

• CAT data link circuit in the machine harness is shorted.

• CAT data link circuit in the machine harness is open.

• An electronic control module which uses the CAT data link has failed. This is unlikely.

1. CHECK FOR ADDITIONAL DIAGNOSTIC CODES

   1. Check for additional CID 0248 diagnostic codes that are logged against the other electronic control modules. This confirms the existence of a communication problem.
      • CID 0091 FMI 09 Throttle Position signal

      • CID 0190 FMI 09 Engine Speed signal

      • CID 0627 FMI 09 Parking Brake signal

      • CID 0700 FMI 09 Transmission Gear indicator

      • CID 0702 FMI 09 Transmission Gear Selector Lever

   2. Check for a harness problem between the two controls that are reporting the CID 0248. Otherwise, Proceed to Step 2.

2. INSPECT THE HARNESS CONNECTORS.

   1. Turn the disconnect switch to the OFF position.

   2. Inspect the connections of the machine harness that are related to the CAT data link. Verify that the connectors are clean and tight.

      Expected Results:The machine harness connectors are clean and tight.

      Results:

      • OK: Connectors of the machine harness are clean and tight. Proceed to Step 3.

      • No: Machine harness connectors are in need of repair. Repair the harness or replace the harness. STOP.

3. CHECK FOR SHORT TO GROUND

   1. The disconnect switch remains in the OFF position.

   2. Disconnect the machine harness from all electronic control modules that use the CAT data link.

   3. At the connector of the machine harness for the main module, measure the resistance between frame ground and the circuits of the CAT data link (contacts 4, 5, 6 and 7).

      Expected Results:The resistance is greater than 5000 ohms.

      Results:

      • OK: Resistance is greater than 5000 ohms. The harness circuit resistance is correct. Proceed to Step 4.

      • No: Resistance is less than 5000 ohms. The machine harness has failed. There is a short between frame ground and the CAT data link in the machine harness. Repair the harness or replace the harness.

4. CHECK FOR A SHORTED HARNESS

   1. The disconnect switch remains in the OFF position.

   2. All related control modules remain disconnected from the machine harness.

   3. Check the line to line resistance of the CAT data link. Perform the following measurements.
      • Measure the resistance between contact "4" and contacts "5", "6" and "7" of the CAT data link at the machine harness connector of the VIMS main module.

      • Measure the resistance between contact "5" and contacts "6" and "7" of the CAT data link at the machine harness connector of the main module.

      • Measure the resistance between contact "6" and contact "7" of the CAT data link at the machine harness connector of the main module.

      Expected Results: The resistance measurements are greater than 5000 ohms.

      Results:

      • OK: Resistance is greater than 5000 ohms. The harness circuit resistance is correct. Proceed to Step 5.

      • No: Resistance is less than 5000 ohms. The machine harness has failed. There is a short between the lines of the CAT data link in the machine harness. Repair the harness or replace the harness. STOP.

5. CHECK FOR SHORT TO +BATTERY

   1. The disconnect switch remains in the OFF position.

   2. All related control modules remain disconnected from the machine harness.

   3. Measure the resistance between the + battery and the circuits of the CAT data link. Measure this resistance at the connector of the machine harness for the ARC.

      Expected Results: The resistance is greater than 5000 ohms.

      Results:

      • OK: Resistance is greater than 5000 ohms. The harness circuit resistance is correct. Proceed to Step 6.

      • No: Resistance is less than 5000 ohms. The machine harness has failed. The CAT data link has a short between the + Battery and the circuits in the machine harness. Repair the harness or replace the harness. STOP.

6. CHECK FOR OPEN HARNESS

   1. The disconnect switch remains in the OFF position.

   2. All related control modules remain disconnected from the machine harness.

   3. At the machine harness connector for the main module, measure the resistance between the CAT data link circuit contacts to the connector contacts of the related electronic control module.

      Expected Results:The resistance is less than 5 ohms.

      Results:

      • OK: Resistance is less than 5 ohms. The CAT data link circuit in the machine harness is correct. The main module has failed. Refer to the Testing and Adjustment, "ARC - Replace" section. STOP.

      • No: Resistance is greater than 5 ohms. The machine harness has failed. The CAT data link circuit is open in the machine harness. Repair the machine harness or replace the machine harness. STOP.

Note: For information on repairing the harness, refer to the Testing And Adjusting, "General Information" section in this manual.