966G Wheel Loader and 972G Wheel Loader Power Train Caterpillar

Illustration 1	g00438123
Transmission Downshift Switch Schematic

The transmission downshift switch has two inputs to the power train electronic control module (ECM). These inputs are normally open (N/O) and normally closed (N/C). During normal operation, one of the inputs is open and the other input is grounded. If both inputs are the same, the power train ECM detects a fault. CID 0621 FMI 03 service code is detected when both inputs are either open or shorted to the +battery. Before performing this procedure refer to table 1 in order to determine the connector and the contact that corresponds to the faulty circuit.

Note: Ensure that the desired fault CID 0621 FMI 03 is active.

Note: The following procedure can create other faults that the power train ECM detects. Ignore these created faults and clear the created faults when CID 0621 FMI 03 is corrected.

1. Check for an open circuit.

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

   2. Disconnect the machine harness connector J1 from the power train ECM.

   3. At the machine harness connector for the power train ECM, check the continuity to ground of the N/C contact and the N/O contact with the transmission downshift switch activated and not activated. Refer to table 1 for the correct switch status.

      Expected Result: The continuity check does not agree with table 1.

      Results:

      • YES - The continuity check does NOT agree with table 1. The harness or the transmission downshift switch is faulty. Proceed to Step 2.

      • NO - The continuity check agrees with table 1. Proceed to Step 3.

2. Check the transmission downshift switch.

   1. Disconnect the machine harness from the transmission downshift switch.

   2. Check the continuity to ground of the N/C contact and the N/O contact with the transmission downshift switch activated and not activated. Refer to table 1 for the correct transmission downshift switch status.

      Expected Result: The continuity check does not agree with table 1.

      Results:

      • YES - The continuity check does not agree with table 1. The transmission downshift switch is faulty. Repair the switch or replace the switch. STOP.

      • NO - Continuity check agrees with table 1. Repair the machine harness or replace the machine harness. STOP.

3. Check for a short to the +battery.

   1. At the machine harness connector for the power train ECM, check the continuity from each of the switch contact wires to the contacts J1-1, J1-6, J1-40 and J2-12.

      Expected Result: Continuity exists between one of the sources of the battery voltage and the switch circuit.

      Results:

      • YES - Continuity exists between one of the sources of battery voltage. The machine harness is faulty. Repair the machine harness or replace the machine harness. STOP.

      • NO - Continuity does not exist between one of the sources of battery voltage and the switch circuit. The machine harness is correct. It is unlikely that the power train ECM is faulty. Exit this procedure and perform CID 0621 FMI 03 again. If the cause is not found, replace the power train ECM. Refer to Testing and Adjusting, "Electronic Control Module (Power Train) - Replace" for more information on replacing the power train ECM. STOP.