D250E Series II, D300E Series II, D350E Series II and D400E Series II Articulated Trucks Power Train Electronic Control System Caterpillar

Illustration 1	g00481473
Schematic Of The Relay For The Backup Alarm

This diagnostic code is recorded when the ECM reads the voltage of the relay circuit as above normal (short to +battery).

The possible causes of this diagnostic code are listed below.

• Wire 321-BR is shorted to the +battery.

• The ECM is faulty. This is unlikely.

This diagnostic code causes the backup alarm to be ON at all times. Ensure that the diagnostic code CID 0144 FMI 03 is active for the backup alarm relay. The relay is connected to wire (321-BR) of the ECM through connector contact J2-37. The return wire (F790-PK) for the relay is connected through connector contact J2-3. The resistance of the relay coil is 360 ohms.

1. CHECK THE SIGNAL CIRCUIT OF THE RELAY FOR A SHORT TO +BATTERY.

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

   2. Disconnect the machine harness from the relay.

   3. Disconnect the machine harness connectors J1 and J2 from the ECM.

   4. At the machine harness connector J1 and J2, measure the resistance from signal contact J2-37 to all other connector contacts.

      Expected Result: Each resistance should be greater than 5000 ohms.

      Results:

      • OK - The resistance is greater than 5000 ohms. The harness circuit is correct. Proceed to 2.

      • NOT OK - There is a short in the machine harness. The short is between the signal contact of the relay and the circuit with the low resistance measurement. Repair the harness or replace the harness. STOP.

2. CHECK IF THE DIAGNOSTIC CODE REMAINS.

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

   2. Reconnect all harness connectors.

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

   4. Check if the CID 0144 FMI 03 diagnostic code is active.

      Expected Result: The CID 0144 FMI 03 diagnostic code for the backup alarm is NOT active.

      Results:

      • YES - The diagnostic code is NO longer active. STOP.

      • NO - The diagnostic code remains active. Exit this procedure and perform this procedure again. If the cause of the diagnostic code is not found, replace the ECM. See Testing And Adjusting, "Electronic Control Module (ECM) - Replace". STOP.