725, 730, 735, 740 and 740 EJECTOR Articulated Trucks Power Train Electronic Control System Caterpillar

Illustration 1	g00756462
Schematic of the Start Relay

This diagnostic code is recorded when the ECM reads the current of the relay circuit as being below normal range (open circuit).

Note: This procedure can cause new diagnostic codes to be recorded. Ignore these created diagnostic codes. Complete the following procedure. Then clear the created diagnostic codes.

Test Step 1. CHECK THE RELAY.

1. Turn the disconnect switch and the key start switch to the ON position. Do not start the engine. Ensure that the diagnostic code for the relay is active.

2. Disconnect the machine harness from the relay.

3. At the machine harness connector for the relay that is being tested, install a jumper wire. Install the jumper wire from contact 2 (306-GN) to contact 1 (E789-PU).

4. Observe the status of the diagnostic code. The diagnostic code is active or the diagnostic code is NOT active.

Expected Result:

The status of the diagnostic code is active and the status of the diagnostic code is NOT active as the jumper is installed and then removed.

Results:

• YES - The circuit is correct.

  Repair: The relay has failed. Repeat the test step "CHECK THE RELAY" in order to verify that the relay has failed. Replace the relay.

  Stop.

• NO - The diagnostic code remains active. Proceed to test step 2.

Test Step 2. CHECK THE RELAY CIRCUIT FOR AN OPEN.

1. The jumper that is between the signal wire and the return wire remains installed.

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

3. Disconnect the machine harness connector J2 from the ECM.

4. At the J2 machine harness connector for the ECM, measure the resistance from contact J2-68 for the relay to contact J2-36 (return contact).

Expected Result:

There should be continuity (less than 5.0 ohms resistance).

Results:

• YES - The machine harness is correct. Proceed to test step 3.

• NO - There is an open circuit in the machine harness.

  Repair: The open circuit is in the signal wire (306-GN) or in return wire (E789-PU) of the machine harness. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 3. CHECK IF THE DIAGNOSTIC CODE REMAINS.

1. The contacts of the harness connectors should be cleaned and inspected.

2. Reconnect all of the harness connectors.

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

4. Clear all of the inactive diagnostic codes.

5. Operate the machine.

6. Stop the machine and place the parking brake switch in the ON position.

7. Observe the status of the diagnostic code. The diagnostic code is active or the diagnostic code is NOT active.

Expected Result:

The diagnostic code is NO longer active.

Results:

• YES - The diagnostic code is NO longer active. 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 has not been corrected. It is unlikely that the ECM has failed.

  Repair: Exit this procedure and perform this diagnostic code again. Recheck the status of the diagnostic code. Replace the ECM if the cause is not found. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  Stop.