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

This fault is recorded when the ARC reads the signal from the engine speed sensor and the ARC determines that the signal is erratic, intermittent or incorrect. The ARC determines the condition by comparing the sensor signal to the engine speed signal from the CAT Data Link.

The possible causes of this fault are in the following list:

• The machine harness (wire 450-YL) is open or shorted between the ARC and the engine speed sensor.

• The engine speed sensor is not installed correctly.

• The engine speed sensor is faulty.

• The ARC is faulty. The ARC is not likely to be faulty.

Service Notes: The engine must be running before the ARC will illuminate the fault present indicator. Ensure that the CID 190 FMI 02 fault is on hold.

1. CHECK THE RESISTANCE OF THE SENSOR.

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

   2. Disconnect the machine harness from the speed sensor.

   3. Measure the resistance between the two contacts of the speed sensor's harness connector.

      Expected Result: The resistance should be between 100 and 500 Ohms.

      Results:

      • OK: The speed sensor is not faulty. Proceed to Step 2.

      • No: The speed sensor has failed. Replace the sensor. Adjust the speed sensor properly when you install the sensor. Refer to Testing and Adjusting, "Speed Sensor - Adjust". STOP.

2. CHECK FOR A SHORTED HARNESS.

   The machine harness remains disconnected from the sensor.

   1. The key start switch and the disconnect switch remain in the OFF position.

   2. Disconnect machine harness connector A from the ARC.

   3. At the machine harness connector for the ARC, measure the resistance between contact A10 (wire 450-YL) and all sources of battery and ground. The other sources of battery power are A1, A3, A4, and A5. The ground source is contact A2.

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

      Results:

      • OK: The resistance is greater than 5000 ohms. The return circuit is correct. Proceed to Step 3.

      • No: The resistance is less than 5000 ohms. Wire 450-YL is faulty. Repair the machine harness or replace the machine harness. STOP.

3. CHECK THE GROUND CIRCUIT.

   1. The disconnect switch remains OFF. The speed sensor remains disconnected from the machine harness. Connector A remains disconnected from the ARC.

   2. At the machine harness connectors for the speed sensor, measure the resistance between wire 451-BR and frame ground.

      Expected Result: The resistance is greater than 2 ohms.

      Results:

      • OK: The resistance is less than 2 ohms. The signal circuit in the machine harness is correct. Proceed to Step 4.

      • No: The resistance is greater than 2 ohms. Wire 451-BR is shorted. Repair the machine harness or replace the machine harness. Proceed to Step 4.a.

4. CHECK THE SIGNAL CIRCUIT.

   The conditions of the previous step remain intact.

   1. At the machine harness connector for the speed sensor, place a jumper from contact 1 (wire 450-YL) to contact 2 (wire 451-BR).

   2. At the harness connectors, measure the resistance between A10 (wire 450-YL) and the frame ground.

      Expected Result: The resistance should be less than 5000 ohms.

      Results:

      • OK: The resistance is less than 5000 ohms. The machine harness is correct. Proceed to Step 5.

      • No: The resistance is greater than 5000 ohms. The machine harness is faulty. Wire 450-YL is open between the speed sensor and the ARC. Repair the machine harness or replace the machine harness.

5. CHECK IF THE FAULT IS STILL PRESENT.

   1. 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. Start the engine and run the engine at low idle.

   5. Enter the service mode of the ARC. Put the CID 0190 FMI 02 service code on hold.

   6. Observe the status of the fault present indicator.

      Expected Result: The fault present indicator is on.

      Results:

      • OK: The fault remains present. Proceed to Step 6.

      • NO: The fault is not present. The fault does not exist at this time. The initial fault was probably caused by a poor electrical connection or a short at one of the harness connectors that was reconnected. Resume normal machine operation. STOP.

6. CHECK THE ADJUSTMENT OF THE SENSOR.

   1. To check the speed sensor adjustment, refer to Testing and Adjusting, "Speed Sensor - Adjust".

   2. Repeat the procedure from the above Step 5.

      Expected Result: The fault remains present.

      Results:

      • OK: The fault remains present. Replace the speed sensor. If conditions are not resolved, proceed to Step 7.

      • No: The fault is not present. Adjusting the speed sensor has corrected the failure. STOP.

7. CHECK IF THE FAULT IS STILL PRESENT.

   1. Remove connectors A and B from the ARC. 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. Enter service mode of the ARC. Clear all inactive faults.

   5. Operate the machine.

   6. Check whether the CID 0190 FMI 02 service code is present.

      Expected Result: The CID 190 FMI 02 service code is present. ("SERV CODE" is showing.)

      Results:

      • OK: The fault has not been corrected. It is unlikely that the ARC is faulty. Perform the test for CID 0190 FMI 02 again. If the cause of the fault is not found, replace the ARC. Refer to Testing and Adjusting, "ARC - Replace". STOP.

      • No: The fault is not present. The fault does not exist at this time. The new speed sensor has corrected the fault. Resume normal machine operation. STOP.