 | |
| Illustration 1 | g00624243 |
Schematic of the Downshift Switch | |
The transmission downshift switch sends two inputs to the transmission electronic control module (ECM). During normal operation, one input is normally open (N/O), and one is normally closed (N/C). An active diagnostic is recorded by the transmission ECM when both switch inputs are open. An active diagnostic is recorded by the transmission ECM, when both switch inputs are closed. The CID 0621 FMI 02 diagnostic code is displayed when this active diagnostic occurs. Before you perform this procedure, refer to Illustration 1 in order to determine the contacts and the wire numbers that correspond to the active circuit.
Note: The wire 202-BK-18 is connected to frame ground.
Note: The active diagnostic should not be present immediately after the key start switch is turned ON. The transmission ECM (2) waits for 30 seconds, before the active diagnostic is recorded.
Test Step 1. CHECK THE CIRCUIT FOR PROPER OPERATION.
- Turn the key start switch to the OFF position.
- Disconnect the harness connector from the ECM.
- At the harness connector, measure the resistance from contact 2 to the switch input.
- Measure the resistance in each of the two positions of the switch.
Expected Result:
One switch position should show resistance of less than 5 ohms. One switch position should show resistance of more than 5,000 ohms.
Results:
- OK - The measured readings are correct. The switch is correct and the switch harness is correct. Proceed to test step 3.
- NOT OK - The measured readings are not correct. The switch is not correct and the switch harness is not correct. Proceed to test step 2.
Test Step 2. CHECK THE SWITCH
- Turn the key start switch to the OFF position.
- Disconnect the harness connector from the ECM.
- At the switch, measure the resistance from contact 2 to the switch input.
- Measure the resistance in each of the two positions of the switch.
Expected Result:
One switch position should show resistance of less than 5 ohms. One switch position should show resistance of more than 5,000 ohms.
Results:
- OK - The measured readings are correct. The switch harness has failed.
Repair: Repair the harness or replace the harness.
Proceed to test step 3.
- NOT OK - The measured readings are not correct. The downshift switch has failed.
Repair: Replace the downshift switch.
Proceed to test step 3.
Test Step 3. CHECK IF THE DIAGNOSTIC CODE IS STILL ACTIVE.
- Remove the connector from the ECM. Inspect the contacts and clean the contacts of the harness connectors.
- Reconnect all harness connectors.
- Turn the key start switch to the ON position.
- Enter service mode of the Caterpillar Monitoring System and clear all inactive diagnostic codes.
- Operate the machine.
- Determine if CID 0621 FMI 02 is present.
Expected Result:
CID 0621 FMI 02 is present.
Results:
- YES - CID 0621 FMI 02 is present.
Repair: The problem has not been corrected. It is unlikely that the ECM has failed. Perform the previous Steps again. If the cause of the diagnostic code is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
Stop.
- NO - CID 0621 FMI 02 is not present.
Repair: The diagnostic code is NOT present. The problem does not exist at this time. The initial problem was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.
Stop.