797 and 797B Off-Highway Truck Power Train Electronic Control System Caterpillar

Illustration 1	g00909958
Schematic of the feedback circuit

The possible causes are listed:

• There is an open in the circuit.

• The ECM has failed. This is unlikely.

Note: The following procedure can create numerous related diagnostic codes. When all harnesses are reconnected, the related diagnostic codes will be shown as being not active. Clear all related diagnostic codes after this procedure is completed.

Note: Ensure that the diagnostic code for the return is active.

Test Step 1. CHECK THE RETURN CIRCUIT FOR AN OPEN.

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

2. Disconnect the J1 and J2 machine harness connector from the ECM.

3. At J1 machine harness connector, measure the resistance from contact J1-2 (wire H802-GY(Grey)) to J2-49 (wire H802-GY(Grey)).

Expected Result:

The resistance should be less than 5 ohms.

Results:

• YES - The resistance is less than 5 ohms. The machine harness is correct. Proceed to test step 2.

• NO - The resistance measurement is NOT correct. There is an open circuit in the machine harness.

  Repair: The open is in the wire for the solenoid signal or in wire (H802-GY(Grey)) of the machine harness. Repair the machine harness or replace the machine harness.

  STOP

Test Step 2. 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 disconnect switch and the key start switch to the ON position.

4. Clear all inactive diagnostic codes.

5. Operate the machine.

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

7. Check if the diagnostic code for the solenoid is 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The diagnostic code is NO longer active.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• YES - The diagnostic code is NO longer active.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.

  Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Also, recheck if the diagnostic code is active for this diagnostic code. If the cause of the diagnostic code is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP