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. CID 0621 FMI 04 service code is recorded when both the N/O and N/C inputs of the transmission downshift switch are grounded.

Note: Ensure that the desired fault CID 0621 FMI 04 is active.

Note: The following procedure can create other faults that the power train ECM will detect. Ignore these created faults and clear the faults when CID 0621 FMI 04 is corrected.

1. Check for an open circuit.

   1. Ensure that the fault is active.

   2. Observe the ON/OFF status of the fault.

   3. Disconnect the connector of the transmission downshift switch from the machine harness.

      Expected Result: The active fault changes from "04" to "03".

      Results:

      • YES - The transmission downshift switch or the switch harness has failed. Repeat Step 1 to verify the transmission downshift switch failure. Repair or replace the switch and or the switch harness.

      • NO - The fault present indicator remains ON. The transmission downshift switch is not the cause of this fault. Proceed to Step 2.

2. Check the harness circuit.

   This test checks the continuity of the entire harness circuit that may be faulty. The transmission downshift switch that was previously checked in Step 1 is included in this test.

   1. Turn the disconnect switch to the OFF position.

   2. Connect the transmission downshift switch of Step 1 to the machine harness.

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

   4. 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 circuit is faulty. There is a short to ground in the machine harness between the power train ECM and the transmission downshift switch. Repair the machine harness or replace the machine harness. STOP.

      • NO - The continuity check agrees with table 1. The harness circuit is correct. It is unlikely that the power train ECM is faulty. Exit this procedure and perform CID 0621 FMI 04 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.