793F CMD Off-Highway Truck (Command for Hauling) Power Train Electronic Control System Caterpillar

Illustration 1	g03338118
Connections of the +8 V sensor supplies

The diagnostic code is recorded when the ECM indicates that the voltage of the sensor supply circuit is too low.

Possible causes of this diagnostic code are listed below:

• The output of sensor supply has an open circuit.

• A sensor has failed.

• The Transmission ECM has failed. This event is unlikely.

Note: Before performing this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean and that all connections are secure. Verify that all connections in the circuit are in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure. The following test procedure may cause other diagnostic codes to be activated. Ignore these created diagnostic codes and clear the diagnostic codes when the problem has been corrected. Verify that the CID 0041 FMI 04 is active before performing this procedure.

Note: Each connector contact should withstand 45 N (10 lb) of pull. Each wire should remain in the connector body. This test checks whether the wire was properly crimped in the contact and whether the contact was properly inserted into the connector.

Use a digital multimeter for the measurements in this procedure.

System Response:

All of the sensors that receive power from the 8 V supply are disabled.

Test Step 1. CHECK THE VOLTAGE AT THE ECM.

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

2. Check the voltage at the harness connector for the ECM from contact J1-44 (wire X800-OR(Orange)) to contact J1-45 (C241-BK(Black)). Use the multimeter probes to measure the voltage. Do NOT disconnect the machine harness from the ECM.

Expected Result:

The voltage is 8.0 ± 0.3 DCV.

Results:

• OK - The voltage is 8.0 ± 0.3 DCV. The sensor supply voltage is correct. Verify that the same diagnostic code is present. If the diagnostic code is still present, the ECM may have failed.

  Repair: A failure of the ECM is unlikely. Exit this procedure and perform this procedure again. Also, recheck if the diagnostic code is active. Prior to replacing and ECM, contact your dealership for possible consultation with Caterpillar. If the ECM requires replacing, see Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP

• NOT OK - The voltage is NOT 8.0 ± 0.3 DCV. The voltage is less than 8.0 ± 0.3 DCV. The sensor supply voltage is NOT correct. Proceed to Test Step 2.

Test Step 2. CHECK FOR A SHORT TO GROUND

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

2. Disconnect the machine harness from the Transmission ECM.

3. At the harness connector for the ECM, measure the resistance between frame ground and contact J1-45 (wire C241-BK(Black)).

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• OK - The resistance is greater than 5000 ohms. Verify that the same diagnostic code is present. If the diagnostic code is still present, the ECM may have failed.

  Repair: A failure of the ECM is unlikely. Exit this procedure and perform this procedure again. Also, recheck if the diagnostic code is active. Prior to replacing an ECM, contact your dealership for possible consultation with Caterpillar. If the ECM requires replacing, see Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP

• NOT OK - Resistance is less than 5 ohms. The machine harness has failed or a sensor has failed. Proceed to Test Step 3.

Test Step 3. DISCONNECT THE SENSORS.

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

2. One at a time, disconnect any sensor that uses the power supply from the machine harness.

3. After disconnecting each sensor, check the resistance from frame ground to contact J1-45 at the harness connector for the Transmission ECM.

Expected Result:

After disconnecting a particular sensor, the resistance changes and the resistance is greater than 5000 ohms.

Results:

• YES - After disconnecting a particular sensor, the resistance changes, and the resistance is greater than 5000 ohms. The sensor that was disconnected has failed.

  Repair: Replace the sensor.

  Proceed to Test Step 4.

• NO - After disconnecting all of the sensors, the resistance is less than 5 ohms. The machine harness is shorted to ground.

  Repair: Repair the machine harness or replace the machine harness.

  STOP

Test Step 4. CHECK IF THE DIAGNOSTIC CODE REMAINS.

1. Inspect the harness connectors. Clean the contacts of the harness connectors. Check the wires for damage to the insulation that is caused by excessive heat, battery acid, or chafing.

2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit.

3. Reconnect all harness connectors in order to make sure that the connectors are fully seated. Also, make sure that the clips for each connector are fastened.

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

5. Operate the machine.

6. Check the status of the diagnostic code.

Expected Result:

The diagnostic code is no longer active.

Results:

• YES - The diagnostic code is not active. The initial diagnostic code was probably caused by a poor electrical connection at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.

  STOP

• NO - The diagnostic code is active. The diagnostic code has not been corrected.

  Repair: A failure of the ECM is unlikely. Exit this procedure and perform this procedure again. Prior to replacing an ECM, always contact your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP