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

Illustration 1	g00527566
Schematic For The Backup Alarm

The ECM applies power to the backup alarm whenever the ECM receives a signal from the reverse direction switch. If the backup alarm is always ON, the harness circuit is shorted to +battery or the ECM is faulty.

1. CHECK FOR SHORT

   1. Turn the key start switch to the OFF position.

   2. Disconnect the connector (two contact) of the start relay from the machine harness.

   3. Turn the key start switch to the ON position. At the machine harness connector for the backup alarm, measure the voltage from contact 1 (wire 321-BR) to frame ground.

      Expected Result: No voltage is present.

      Results:

      • Voltage is present. Go to Step 2.

      • Voltage is NOT present. The fault is not currently present. Clean the contacts of the connector. Reconnect the backup alarm to the machine harness. Clear the CID 0637 FMI 03 service code. The initial fault was probably caused by a poor electrical connection or an intermittent short to +battery. Resume normal machine operation and watch for the recurrence of this fault.

2. CHECK THE SIGNAL VOLTAGE.

   1. Turn the key start switch to the OFF position.

   2. The backup alarm remains disconnected from the machine harness. Disconnect the ECM from the machine harness.

   3. Disconnect the ECM from the machine harness. Turn the key start switch to the ON position.

   4. Repeat the measurement of Step 1. At the machine harness connector for the backup alarm, measure the voltage from contact 1 (wire 321-BR) to frame ground.

      Expected Result: NO voltage is present.

      Results:

      • YES - Voltage is NOT present. There is a fault. It is unlikely that the ECM is faulty. Perform the previous Steps again. If the cause of the fault is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

      • NO - Voltage is present. wire 321-BR is shorted in the machine harness. Repair the machine harness or replace the machine harness.