WORM-DR CRIC-YM 2826623 - Caterpillar

Table 1
Switch Circuits at the ECM Connector
CID
Switch Switch
State ECM Connector
Contact Switch
Connector
Contact Wire Status
CID 0621
Downshift
Switch Deactivated J1-20 N/O N/O (1) F781-BR(Brown) O(2)
J1-29 N/C N/C (3) F784-YL(Yellow) G(4)
Activated J1-20 N/O N/O F781-BR(Brown) G
J1-29 N/C N/C F784-YL(Yellow) O
(1) N/O is Normally Open.
(2) "O" is Open.
(3) N/C is Normally Closed.
(4) "G" is Grounded.When the transmission fails to downshift, the transmission gear that is displayed by the Caterpillar Monitoring System does not change. The downshift switch is a push button switch. The switch has two inputs to the ECM. During normal operation, one input is open and one input is closed to ground. This failure can occur when both inputs are in the same state and the switch is activated. Other possible causes are listed below:
The gear that is desired is not available.
Other diagnostic codes are causing additional failures.
There is a open wire between the normally open contact of the switch and the ECM.
There is a grounded wire between the normally closed contact of the switch and the ECM.
The switch has failed.
The ECM has failed. This is unlikely.Note: The symptoms for CID 0622 FMI 02 are similar.Test Step 1. CHECK FOR DIAGNOSTIC CODES.View the logged diagnostic codes.Expected Result:Diagnostic codes are active.Results:
YES - Diagnostic codes are active.Repair: Exit this test procedure and perform the diagnostic code procedures. Operate the machine and verify that the problem has been repaired.STOP
NO - No diagnostic codes are active. Proceed to Test Step 2.Test Step 2. CHECK THE CIRCUIT FOR PROPER OPERATION.
Turn the key start switch to the ON position.
Access the "Component Data Display Mode". View the value that is displayed for CID 0621. There are values for the normally open circuit and the normally closed circuit. See Testing and Adjusting, "Calibration" for a list of the values that are visible.
Press the downshift switch with the lever in the forward position. Press the downshift switch with the lever in the reverse position. Expected Result:The value that is displayed changes from "OC" to "CO".Results:
OK - The value that is displayed changes from "OC" to "CO". Proceed to Test Step 3.
NOT OK - The value that is displayed does not change from "OC" to "CO".Repair: The normally open circuit or the normally closed circuit has failed. Exit this procedure. Perform the procedure for CID 0621 FMI 02. Operate the machine and verify that the problem has been repaired.STOPTest Step 3. CHECK THE OPERATION OF THE TRANSMISSION SHIFT LEVER.
Operate the machine.
Press and release the downshift switch. Press and release the upshift switch. Expected Result:The transmission operates properly.Results:
OK - The transmission operates properly. The problem does not exist at this time. The initial problem was caused by a poor connection at one of the harness connectors. Resume normal machine operation.STOP
NOT OK - The transmission does not operate properly.Repair: Exit this procedure and perform the diagnostic code procedure again. If the problem persists, the ECM may have failed. Prior to replacing an ECM, always contact your dealership's Technical Communicator for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See theTesting and Adjusting, "Electronic Control Module