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| Illustration 1 | g01076278 |
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Schematic of the backup alarm | |
The Power Train/Chassis Electronic Control Module (ECM) applies power to the backup alarm relay when the ECM receives a reverse signal from the shift lever position sensor.
One of the following conditions can cause the backup alarm to remain off:
- The backup alarm has failed.
- The machine harness has failed.
- The machine harness is shorted to frame ground.
- The machine harness is shorted to +battery.
- The ECM has failed.
- The backup alarm relay has failed.
Test Step 1. CHECK THE BACKUP ALARM
- Turn the key start switch and the battery disconnect switch to the OFF position.
- Disconnect the backup alarm from the machine harness.
- Use jumpers to connect the respective terminals of the backup alarm to the +battery source and frame ground.
Expected Result:
The backup alarm sounds when +battery is applied.
Results:
- OK - The backup alarm sounds when +battery is applied. The backup alarm operates correctly. Proceed to Test Step 2.
- NOT OK - The backup alarm does not sound when +battery is applied.
Repair: The backup alarm has failed. Replace the backup alarm. Verify that the new backup alarm corrects the problem.
STOP
Test Step 2. CHECK THE ALARM CIRCUIT FROM THE RELAY FOR AN OPEN
- Disconnect the machine harness connector from the relay.
- The machine harness connector from the backup alarm remains disconnected.
- Measure the resistance from contact 1 (wire 612-GY(Grey)) of the backup alarm connector to contact 4 of the machine harness connector for the relay.
Expected Result:
The resistance that is measured is less than 5 ohms.
Results:
- OK - The resistance measured is less than 5 ohms. The machine harness is correct. Proceed to Test Step 3.
- NOT OK - The resistance that is measured is greater than 5 ohms. The machine harness for the backup alarm has failed.
Repair: Repair the machine harness or replace the machine harness.
STOP
Test Step 3. CHECK THE SIGNAL CIRCUIT FROM THE ECM TO THE RELAY FOR AN OPEN
- Disconnect the machine harness connectors J1 and J2 from the ECM.
- Disconnect the machine harness from the relay.
- Measure the resistance from contact J2-3 (wire E790-PK(Pink)) of the ECM to contact 2 (wire E790-PK(Pink)) of the relay.
- Measure the resistance from contact J2-37 (wire 321-BR(Brown)) of the ECM to contact 5 (wire 321-BR(Brown)) of the relay.
Expected Result:
The resistance should measure less than 5 ohms.
Results:
- OK - The resistance is less than 5 ohms. Proceed to Test Step 4.
- NOT OK - The resistance is greater than 5 ohms. The machine harness has failed.
Repair: Repair machine harness or replace machine harness.
STOP
Test Step 4. CHECK THE RELAY COIL
- Check the resistance at contacts 5 and 2 of the relay.
Expected Result:
The resistance should be between 288 ohms to 398 ohms.
Results:
- OK - The resistance is correct. Proceed to Test Step 5.
- NOT OK - The resistance is not within the specified range. The relay has failed.
Repair: Replace relay.
STOP
Test Step 5. CHECK THE RELAY CONTACTS
- Check the resistance at contacts 1 and 3 of the relay.
Expected Result:
The resistance should be less than 5 ohms.
Results:
- OK - The resistance is less than 5 ohms. Proceed to Test Step 6.
- NOT OK - The resistance is greater than 5 ohms. The relay has failed.
Repair: Replace the relay.
STOP
Test Step 6. CHECK THE RELAY CONTACTS
- Check the resistance at contacts 1 and 4 of the relay.
Expected Result:
The resistance should be greater than 5 ohms.
Results:
- OK - The resistance is greater than 5 ohms. Proceed to Test Step 7.
- NOT OK - The resistance is less than 5 ohms. The relay has failed.
Repair: Replace the relay.
STOP
Test Step 7. CHECK POWER SUPPLY
- Turn the battery disconnect switch and the key start switch to the ON position.
- Check for 24 volt supply at contact 1 (wire 120-YL(Yellow)) of the relay.
Expected Result:
The voltage should be 24 volt supply at (wire 120-YL(Yellow)).
Results:
- OK - The voltage is 24 volt supply at (wire 120-YL(Yellow)). The machine harness is correct. Proceed to Test Step 8.
- NOT OK - The voltage is less than +battery.
Repair: Repair machine harness or replace machine harness.
STOP
Test Step 8. CHECK THE SIGNAL CIRCUIT OF THE RELAY FOR A SHORT TO FRAME GROUND
- Turn the battery disconnect switch and the key start switch to the OFF position.
- At the J1 and J2 machine harness connectors for the ECM, measure the resistance from the signal contact of the relay J2-37 (wire 321-BR(Brown)) to all possible sources of frame ground.
- At the J1 and J2 machine harness connectors for the ECM, measure the resistance from the return contact of the relay J2-3 (wire E790-PK(Pink)) to all possible sources of frame ground.
Expected Result:
Each resistance should be greater than 5 ohms.
Results:
- OK - Each resistance is greater than 5 ohms. Proceed to Test Step 9.
- NOT OK - The resistance is less than 5 ohms. The machine harness has failed.
Repair: Repair the machine harness or replace the machine harness.
STOP
Test Step 9. CHECK THE SIGNAL CIRCUIT OF THE BACKUP ALARM FOR A SHORT TO +BATTERY
- At the connector of the backup alarm measure the resistance between to contact 1 (wire 612-GY(Grey)) to all possible sources of +battery.
Expected Result:
Each resistance should be greater than 5 ohms.
Results:
- OK - The resistance is greater than 5 ohms. The ECM may have failed. Proceed to Test Step 10.
- NOT OK - The resistance is less than 5 ohms. The machine harness has failed.
Repair: Repair the machine harness or replace the machine harness.
STOP
Test Step 10. CHECK IF THE PROBLEM REMAINS
- Inspect the contacts of the harness connectors and clean the harness connectors.
- Reconnect all the harness connectors.
- Turn the battery disconnect switch and the key start switch to the ON position.
- Operate the machine.
- Check to see if the fault still occurs.
Expected Result:
The fault is present.
Results:
- YES - The fault is present. The fault has not been corrected. The ECM may have failed.
Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the cause of the fault is not found, replace the ECM. Refer to Systems operation, Troubleshooting, Testing and Adjusting, "Electronic Control Module (ECM) - Replace" for the machine that is being serviced.
STOP
- NO - The fault is no longer present. The fault does not exist at this time.
Repair: The initial fault 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