The following procedure is used to troubleshoot the parking brake limit switch. The ECM does not diagnose problems with the parking brake limit switch.
The parking brake limit switch is used to signal the status of the parking brake to the ECM. When the parking brake is applied, the contacts of the parking brake limit switch close. The closing of the contacts applies a ground signal to the ECM.
The possible causes of a problem with the parking brake limit switch are listed:
- The return wire 202-BK is open.
- The wire F765-BR is open.
- The parking brake limit switch is faulty.
- The ECM is faulty. This is unlikely.
Test Step 1. CHECK THE CIRCUIT FOR PROPER OPERATION
- Turn the key start switch to the OFF position.
- Disconnect the machine harness from the ECM.
- At the machine harness connector, measure the resistance from contact 13 to contact 2 (ground).
- Observe the measurement while you depress the parking brake.
Expected Result:
When the parking brake is depressed, the resistance should measure less than 5 ohms. When the parking brake is NOT depressed, the resistance should measure more than 5000 ohms.
Results:
- OK - The resistance is within an acceptable range. The circuit is functioning correctly. Proceed to test step 3.
- NOT OK - The resistance is not within an acceptable range. The switch has failed or the machine harness has failed. Proceed to test step 2.
Test Step 2. CHECK THE CIRCUIT OF THE SWITCH
- Turn the key start switch to the OFF position.
- Disconnect the wire F765-BR from the parking brake limit switch. Disconnect the wire 202-BK from the parking brake limit switch.
- Measure the resistance between the NO terminal and the common terminal of the switch.
- Observe the measurement while you depress the parking brake.
Expected Result:
When the parking brake is depressed, the resistance should measure less than 5 ohms. When the parking brake is NOT depressed, the resistance should measure more than 5000 ohms.
Results:
- OK - The resistance is within an acceptable range. The auto/manual switch is functioning correctly. The machine harness is faulty.
Repair: Repair the machine harness or replace the machine harness.
Stop.
- NOT OK - The resistance is not within an acceptable range. The switch has failed.
Repair: Repair the switch or replace the switch.
Stop.
Test Step 3. VERIFY PROPER OPERATION OF THE CIRCUIT
- Remove the connector from the ECM. Inspect the contacts and clean the contacts of the harness connectors.
- Reconnect all harness connectors.
- Test the operation of the parking brake limit switch.
Expected Result:
The parking brake limit switch operates correctly.
Results:
- NO - The parking brake limit switch does NOT operate correctly.
Repair: The problem has not been corrected. It is unlikely that the ECM has failed. Perform the previous Step again. If the cause of the problem is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
Stop.
- YES - The parking brake limit switch operates correctly.
Repair: 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.