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| Illustration 1 | g00925916 |
Schematic of the Limit switch (parking brake)
This switch has two inputs to the ECM. The two inputs are normally open and normally closed. During normal operation, one of the inputs is open. The other input is grounded. When a circuit is measured with a voltmeter, an open circuit will measure approximately 5 DCV and a closed circuit will measure approximately 0 DCV.
An FMI 03 diagnostic code is recorded when the status of both the inputs are open.
The possible causes of this diagnostic code are listed below:
- The return circuit (wire J764-BR) is open.
- The "NORMALLY OPEN" signal circuit (wire C743-PK) is open.
- The "NORMALLY CLOSED" signal circuit (wire C744-PU) is open.
- The "NORMALLY OPEN" signal circuit (wire C743-PK) is shorted to the + battery.
- The "NORMALLY CLOSED" signal circuit (wire C744-PU) is shorted to the + battery.
- The parking brake switch has failed.
- The ECM has failed. This is unlikely.
Test Step 1. CHECK THE GROUND CIRCUIT AT THE SWITCH
- Turn the key start switch to the OFF position.
- Measure the resistance between contact "COMMON" (wire J764-BR) at the switch and frame ground.
Expected Result:
The resistance should be less than 5 ohms.
Results:
- OK - The resistance is less than 5 ohms. Proceed to Test Step 3.
- NOT OK - The resistance is greater than 5 ohms. Proceed to Test Step 2.
Test Step 2. CHECK THE GROUND CIRCUIT FOR AN OPEN
- Disconnect the machine harness connectors from the ECM.
- Measure the resistance between contact J1-45 (wire J764-BR) and contact "COMMON" (wire J764-BR) at the switch.
Expected Result:
The resistance should be less than 5 ohms.
Results:
- OK - The resistance is less than 5 ohms.
Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the diagnostic code is still present, replace the ECM. Refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
Stop.
- NOT OK - The resistance is greater than 5 ohms.
Repair: The return circuit (wire J764-BR) is open in the machine harness. Repair the machine harness or replace the machine harness.
Stop.
Test Step 3. CHECK THE SWITCH IN THE OFF POSITION
- Place the switch in the OFF position.
- Measure the resistance between contact "COMMON" and contact "NORMALLY OPEN" of the switch.
- Measure the resistance between contact "COMMON" and contact "NORMALLY CLOSED" of the switch.
Expected Result:
The resistance should be less than 5 ohms between contact "COMMON" and contact "NORMALLY OPEN" and the resistance should be greater than 5000 ohms between contact "COMMON" and contact "NORMALLY CLOSED".
Results:
- OK - The resistance is less than 5 ohms between contact "COMMON" and contact "NORMALLY OPEN" and the resistance is greater than 5000 ohms between contact "COMMON" and contact "NORMALLY CLOSED". Proceed to Test Step 4.
- NOT OK - The resistance is not within an acceptable range. The switch has failed.
Repair: Replace the parking brake switch. Verify that the new switch corrects the diagnostic code.
Stop.
Test Step 4. CHECK THE SWITCH IN THE ON POSITION
- Place the switch in the ON position.
- Measure the resistance between contact "COMMON" and contact "NORMALLY OPEN" of the switch.
- Measure the resistance between contact "COMMON" and contact "NORMALLY CLOSED" of the switch.
Expected Result:
The resistance should be greater than 5000 ohms between contact "COMMON" and contact "NORMALLY OPEN" and the resistance should be less than 5 ohms between contact "COMMON" and contact "NORMALLY CLOSED".
Results:
- OK - The resistance is greater than 5000 ohms between contact "COMMON" and contact "NORMALLY OPEN" and the resistance is less than 5 ohms between contact "COMMON" and contact "NORMALLY CLOSED". Proceed to Test Step 5.
- NOT OK - The resistance is not within an acceptable range. The switch has failed.
Repair: Replace the parking brake switch. Verify that the new switch corrects the diagnostic code.
Stop.
Test Step 5. CHECK THE SIGNAL CIRCUITS FOR AN OPEN
- Disconnect the machine harness connectors from the ECM.
- Measure the resistance between contact J2-52 (wire C744-PU) and contact "NORMALLY CLOSED" (wire C744-PU) at the switch.
- Measure the resistance between contact J2-53 (wire C743-PK) and contact "NORMALLY OPEN" (wire C743-PK) at the switch.
Expected Result:
The resistances should be less than 5 ohms.
Results:
- OK - The resistances are less than 5 ohms. Proceed to Test Step 6.
- NOT OK - The resistance is greater than 5 ohms on one of the readings.
Repair: The circuit with the high resistance is open in the machine harness. Repair the machine harness or replace the machine harness.
Stop.
Test Step 6. CHECK THE SIGNAL CIRCUITS FOR A SHORT TO THE + BATTERY
- Measure the resistance between contact J2-52 (wire C744-PU) and contact J1-38 (wire 111-RD).
- Measure the resistance between contact J2-53 (wire C743-PK) and contact J1-38 (wire 111-RD).
Expected Result:
The resistances should be greater than 5000 ohms.
Results:
- OK - The resistances are greater than 5000 ohms.
Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the diagnostic code is still present, replace the ECM. Refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
Stop.
- NOT OK - The resistance is less than 5000 ohms on at least one of the readings.
Repair: The circuit with the low resistance is shorted in the machine harness. Repair the machine harness or replace the machine harness.
Stop.