24H Motor Grader Transmission Electronic Control System And Hydraulic Calibrations Caterpillar

Illustration 1	g00527566
Schematic For The Backup Alarm

If the backup alarm is always OFF one of the following four events has happened:

• The backup alarm is faulty.

• The harness circuit is open.

• The harness circuit is shorted to ground.

• The ECM is faulty.

1. CHECK THE BACKUP ALARM.

   1. Disconnect the backup alarm from the machine harness.

   2. Use jumpers to connect the respective terminals of the backup alarm to +battery and ground.

      Expected Result: The backup alarm does NOT sound as the jumper is installed.

      Results:

      • YES - The backup alarm does NOT sound. The backup alarm is faulty. Replace the backup Alarm. STOP.

      • NO - The backup alarm sounds. The backup alarm operates correctly. Proceed to Step 2.

2. CHECK FOR SHORTED HARNESS

   1. Turn the disconnect switch to the OFF position.

   2. The backup alarm remains disconnected.

   3. At machine harness connector for the ECM, measure the resistance between connector J2-37 (wire 321-BR) and frame ground.

      Expected Result: Resistance is less than 5000 Ohms.

      Results:

      • OK - Resistance is less than 5000 Ohms (continuity). The machine harness is faulty. Wire 321-BR is shorted to ground in the machine harness. Repair the machine harness or replace the machine harness. STOP.

      • NOT OK - Resistance is greater than 5000 Ohms (no continuity). Harness circuit resistance is correct. Proceed to Step 3.

3. CHECK FOR OPEN HARNESS

   1. The disconnect switch remains OFF.

   2. The backup alarm and the ECM remain disconnected from the machine harness.

   3. At the machine harness connector for the ECM, place a jumper from contact J2-37 (wire 321-BR) to contact 3 (wire 975-WH).

   4. At the machine harness for the backup alarm, measure the resistance between wire 975-WH and wire 321-BR.

      Expected Result: Resistance is greater than 5000 Ohms.

      Results:

      • YES - Resistance is greater than 5000 Ohms (no continuity). The harness circuit is faulty. Wire 975-WH or wire 321-BR is open. The open is in the machine harness between the ECM and the backup alarm. Repair the machine harness or replace the machine harness.

      • NO - Resistance is less than 5000 Ohms (continuity). It is unlikely that the ECM is faulty. Exit this procedure and perform this procedure again. If the cause of the fault is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace". STOP.