AD55B Underground Articulated Truck Power Train Electronic Control System Caterpillar

Illustration 1	g01340899
Schematic of the backup alarm

When the shift lever is in the REVERSE position, a signal is sent to the Power Train/Chassis Electronic Control Module (ECM). The Power Train/Chassis ECM switches the backup alarm relay coil to frame ground. When the backup alarm relay is energized +battery is applied to the backup alarm.

If the backup alarm is always off, check these items:

• The circuit breakers have tripped.

• The backup alarm has failed.

• The machine harness has failed.

• The machine harness is shorted to frame ground.

• The backup alarm relay has failed.

• The Power Train/Chassis ECM has failed.

Note: Ensure no diagnostic codes are active before performing this procedure.

Test Step 1. CHECK CIRCUIT BREAKERS

1. Check the status of Circuit Breaker 6 and Circuit Breaker 13.

Expected Result:

Circuit Breaker 6 and Circuit Breaker 13 are OK.

Results:

• YES - Circuit Breaker 6 and Circuit Breaker 13 are OK. Proceed to Test Step 2.

• NO - Circuit Breaker 6 or Circuit Breaker 13 are NOT OK. Machine harness has failed.

  Repair: Identify short to frame ground. Repair machine harness or replace machine harness. Reset Circuit Breaker when repair is carried out.

  STOP

Test Step 2. CHECK THE POWER SUPPLY TO THE BACKUP ALARM

1. Remove the backup alarm.

2. Turn the battery disconnect switch and the key start switch to the ON position.

3. Move the transmission control to the REVERSE position.

4. At the machine harness connector for the backup alarm, check for +battery between contact 1 (wire 612-GY) and contact 2 (wire 202-BK).

Expected Result:

The voltage should be +battery between contact 1 (wire 612-GY) and contact 2 (wire 202-BK).

Results:

• YES - The voltage is +battery between contact 1 (wire 612-GY) and contact 2 (wire 202-BK). The machine harness is correct.

  Repair: Replace the backup alarm.

  STOP

• NO - The voltage is less than +battery between connector contact 1 (wire 612-GY) and connector contact 2 (wire 202-BK). Proceed to Test Step 3.

Test Step 3. CHECK THE BACKUP ALARM FRAME GROUND CIRCUIT

1. Turn the key start switch and the battery disconnect switch to the OFF position.

2. At the machine harness connector for the backup alarm, measure the resistance from contact 2 (wire 202-BK) to frame ground.

Expected Result:

The resistance measured is less than 5 ohms.

Results:

• YES - The resistance measured is less than 5 ohms, the harness is correct. Proceed to Test Step 4.

• NO - The resistance measured is greater than 5 ohms, repair the machine harness or replace the machine harness.

  Repair: Repair machine harness or replace machine harness.

  STOP

Test Step 4. CHECK THE ALARM CIRCUIT FROM THE BACKUP ALARM RELAY FOR AN OPEN

1. The battery disconnect switch and the key start switch remain in the OFF position.

2. Remove the backup alarm relay.

3. At the machine harness connector for the backup alarm, place a jumper wire between connector contact 1 (wire 612-GY) and connector contact 2 (wire 202-BK).

4. At the machine harness connector for the backup alarm relay, measure the resistance from connector contact 4 (wire 612-GY) to frame ground.

Expected Result:

The resistance is less than 5 ohms.

Results:

• YES - The resistance measured is less than 5 ohms. Proceed to Test Step 5.

• NO - The resistance measured is greater than 5 ohms. The machine harness has failed.

  Repair: Repair the machine harness or replace the machine harness.

  STOP

Test Step 5. CHECK THE POWER SUPPLY TO THE BACKUP ALARM RELAY

1. Turn the battery disconnect switch and the key start switch to the ON position.

2. At the machine harness connector for the backup alarm relay, check the +battery at connector contact 1 (wire 120-YL) and connector contact 5 (wire 126-PK).

Expected Result:

+Battery voltage is present at connector contact 1 (wire 120-YL) and connector contact 5 (wire 126-PK).

Results:

• YES - +Battery voltage is present at connector contact 1 (wire 120-YL) and connector contact 5 (wire 126-PK). Proceed to Test Step 6.

• NO - The voltage is less than +battery at connector contact 1 (wire 120-YL) and/or connector contact 5 (wire 126-PK). The machine harness has failed or, Circuit Breaker 6 and/or Circuit Breaker 13 is NOT OK.

  Repair: Repair machine harness or replace machine harness. Reset Circuit Breakers after the repair is carried out.

  STOP

Test Step 6. CHECK THE BACKUP ALARM RELAY "COIL"

1. Measure the resistance between contact 5 and contact 2 of the backup alarm relay.

Expected Result:

The resistance should be between 288 ohms and 398 ohms.

Results:

• YES - The resistance is correct. Proceed to Test Step 7.

• NO - The resistance is not within the specified range. The backup alarm relay has failed.

  Repair: Replace the backup alarm relay.

  STOP

Test Step 7. CHECK THE RETURN CIRCUIT FOR OPEN

1. The backup alarm relay remains removed.

2. Turn the key start switch and the disconnect switch to the OFF position.

3. Move the transmission control to the REVERSE position.

4. Turn the disconnect switch and the key start switch to the ON position.

5. At the machine harness connector for the backup alarm relay measure the resistance from connector contact 2 (wire 331-OR) J2-12 to frame ground.

Expected Result:

The resistance should be less than 5 ohms.

Results:

• YES - The resistance measured is less than 5 ohms. Proceed to Test Step 8.

• NO - The resistance measured is greater than 5 ohms. The machine harness has failed.

  Repair: Repair the machine harness or replace the machine harness.

  STOP

Test Step 8. CHECK IF THE PROBLEM REMAINS

1. Inspect the contacts of the harness connectors and clean the harness connectors.

2. Reconnect all the harness connectors.

3. Operate the machine.

4. 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 Power Train/Chassis ECM may have failed.

  Repair: It is unlikely that the Power Train/Chassis ECM has failed. Exit this procedure and perform this procedure again. If the cause of the fault is not found, replace the Power Train/Chassis ECM. Refer to Systems Operation, Troubleshooting, Testing and Adjusting, "Electronic Control Module ECM - Replace".

  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