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

Illustration 1	g00600352
Schematic Of The Secondary Steering Relay

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:

• Wire 728-BU shorted to +battery.

• The relay is faulty.

• The ECM is faulty. This is unlikely.

Note: Ensure that CID 0420 FMI 03 for the relay is active.

This diagnostic code causes the secondary steering system to be energized at all times.

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

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

   2. Disconnect the relay with the diagnostic code from the machine harness.

   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 J1-10 (wire 728-BU) to all possible sources of +battery. The possible sources of positive voltage are connector contacts: J1-1 (wire 126-PK), J1-4 (wire A958-WH), J1-6 (wire 126-PK), J1-8 (wire 306-GN), J1-10 (wire 728-BU), J1-11 (wire 705-PK), J1-12 (703-BU), J1-17 (wire 904-BU), J1-18 (wire 704-GY), J2-1 (wire K746-PK), J2-2 (wire 368-OR), J2-7 (wire G870-GY), J2-8 (wire K745-YL), J2-13 (wire G705-GN), J2-19 (wire G704-YL) and J2-37 (wire 321-BR).

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

      Results:

      • YES - The resistance measurements are correct. Proceed to 2.

      • NO - The resistance measurements are not correct. The short is between the signal contact J1-10 (wire 728-BU) and the circuit with the low resistance measurement. Repair the harness or replace the harness. STOP.

2. CHECK THE RELAY.

   1. Turn the key start switch and the disconnect switch to the ON position. DO NOT start the engine.

   2. Ensure that the CID 0420 FMI F03 is on-hold.

   3. Observe the status of the diagnostic code. "SERV CODE" will be showing or "SERV CODE" will not be showing.

   4. Disconnect the machine harness from the backup alarm relay.

      Expected Result: The "SERV CODE" indicator is no longer illuminated when the relay is disconnected.

      Results:

      • YES - The "SERV CODE" indicator is no longer illuminated when the relay is disconnected. Proceed to 3.

      • NO - The "SERV CODE" indicator remains illuminated when the relay is disconnected. The relay has failed. Replace the relay. STOP.

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

   4. Enter the service mode of the Caterpillar Monitoring System and clear all the inactive diagnostic codes.

   5. Attempt to operate the machine in all gears. All gears may not be available.

   6. Stop the machine and engage the parking brake.

   7. Observe the status of CID 0420 FMI 03.

      Expected Result: CID 0420 FMI 03 for the relay is NO longer present. The "SERV CODE" indicator is NO longer illuminated.

      Results:

      • YES - The diagnostic code is NO longer present. The original problem was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Watch for a recurrence. STOP.

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