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 circuit as above normal (short to ground).

Possible causes of this diagnostic code are listed:

• Wire 728-BU shorted to ground.

• The relay is faulty.

• The ECM is faulty. This is unlikely.

This diagnostic code causes the backup alarm to be OFF at all times.

Ensure that CID 0420 FMI 06 is active for the secondary steering relay. The relay is connected to the ECM through the harness connector contact J1-10 (wire 728-BU). The return wire (F789-PU) for the relay is connected through the harness to contact J1-7 at the ECM. The resistance of the relay coil is 360 ohms.

Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code is corrected.

1. CHECK THE RELAY.

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

   2. Ensure that the CID 420 FMI 06 is on-hold.

   3. Observe the status of the "SERV CODE" indicator. The "SERV CODE" will be showing or the "SERV CODE" will not be showing.

   4. Disconnect the machine harness from the secondary steering relay.

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

      Results:

      • OK - The "SERV CODE" is no longer showing. The relay has failed. Replace the relay. STOP.

      • NO - The "SERV CODE" is still showing. Proceed to 2.

2. CHECK THE CIRCUIT FOR A SHORT TO GROUND.

   1. Turn the key start 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 J1 machine harness connector, measure the resistance from the signal contact J1-10 (wire 728-BU) to all possible sources of ground.

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

      Results:

      • OK - The resistance is correct. Proceed to 3.

      • NOT OK - The resistance is not correct. Repair the harness or replace the harness. STOP.

3. CHECK IF THE DIAGNOSTIC CODE REMAINS.

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

   2. Reconnect all harness connectors.

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

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

   5. Operate the machine.

   6. Check if the CID 0420 FMI 06 for the relay is present. "SERV CODE" is showing.

      Expected Result: The CID 0420 FMI 06 for the relay is NOT present. The "SERV CODE" is NOT showing.

      Results:

      • YES - The diagnostic code is NOT present. 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 remains present. The "SERV CODE" is still showing. 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.