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 as above normal (short to ground).

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. 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 changes to "NOT active" when the relay is disconnected.

Results:

• YES - The circuit is correct. The relay has failed.

  Repair: Repeat this test "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 SIGNAL CIRCUIT OF THE RELAY FOR A SHORT.

1. Turn the disconnect switch and 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 and J2 machine harness connectors for the ECM, measure the resistance from the signal contact of the relay J2-68 (wire 306-GN) to ground. The possible sources of ground are contacts: 725 and 730 machines J1-12, J2-2, J2-12, J2-13, J2-22, J2-36, J2-41, J2-46, J2-49, J2-52, J2-56, J2-59, J2-69 and frame ground. 735 machines J1-12, J1-20, J2-2, J2-12, J2-13, J2-18, J2-22, J2-36, J2-46, J2-49, J2-52, J2-56, J2-59 and J2-69. 740 machines J1-12, J1-20, J2-2, J2-12, J2-13, J2-22, J2-36, J2-46, J2-56, J2-59 and J2-69.

Expected Result:

Each resistance should be greater than 5000 ohms.

Results:

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

• NO - There is a short in the machine harness.

  Repair: The short is between the signal contact of the relay and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 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 to the ON position.

4. Clear all of the inactive diagnostic codes.

5. Operate the machine.

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

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

Expected Result:

The diagnostic code for the relay is NO longer present.

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 and/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. The diagnostic code is active or the diagnostic code is NOT active. Replace the ECM if the cause is not found. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  Stop.