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 current of the relay as being below normal.

The possible causes of this diagnostic code are listed:

• Wire 728-BU open.

• The relay is faulty.

• The ECM is faulty. This is unlikely.

Note: Ensure that the CID 0420 FMI 05 for the relay is present. The "SERV CODE" is showing.

This diagnostic code prevents the secondary steering system from being energized.

1. CHECK THE RESISTANCE OF THE RELAY.

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

   2. Disconnect the machine harness from the suspect relay.

   3. Measure the resistance between the two contacts of the connector for the relay.

      Expected Result: The resistance should be approximately 360 ohms.

      Results:

      • YES - The relay resistance is correct. Either the signal wire (728-BU) for the relay or the return wire (wire F789-PU) for the relay is open in the harness. Proceed to 2.

      • NO - The relay has failed. Replace the relay. STOP.

2. CHECK THE RELAY FOR AN OPEN CIRCUIT.

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

   2. Reconnect the relay to 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 contact J1-7 (wire F789-PU).

      Expected Result: The resistance measures approximately 360 ohms.

      Results:

      • YES - The resistance does measures approximately 360 Ohms. The resistance of the relay is correct. Suspect an intermittent diagnostic code. Reconnect the connectors and recheck the system. Proceed to 3.

      • NO - The resistance is not correct. The open is in wire (728-BU) for the relay signal or in wire (F789-PU) of the machine harness. Check continuity on each of the circuits. Repair the machine harness or replace the machine harness. 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. Operate the machine and then observe if the diagnostic code reappears.

   5. Observe the status of CID 0420 FMI 05 for the relay.

      Expected Result: The diagnostic code for the relay is NO longer present. The "SERV CODE" is NOT showing.

      Results:

      • YES - The fault is NOT present. The "SERV CODE" is NOT showing. The diagnostic code does not exist at this time. The initial diagnostic code 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.

      • NO - The diagnostic code is still present ("SERV CODE" showing). 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. See Testing And Adjusting, "Electronic Control Module (ECM) - Replace". STOP.