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

Illustration 1	g03338118
Connections of the +8 V sensor supplies

This diagnostic code is recorded when the ECM reads the voltage of the sensor supply circuit as higher than normal.

Possible causes of this diagnostic code are listed below:

• The output of the sensor supply has shorted to the + battery circuit.

• The Transmission ECM has failed. This failure 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.

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.

Test Step 1. CHECK THE VOLTAGE AT A COMPONENT

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

2. Disconnect the machine harness connector from one of the sensors in the Illustration above.

3. At the harness connector for the sensor, measure the voltage from contact A (wire X800-OR(Orange)) to contact B (wire C241-BK(Black)).

Expected Result:

The voltage measurement is 8.0 ± 0.3 VDC.

Results:

• OK - The voltage measurement is 8.0 ± 0.3 VDC. The voltage is correct. Proceed to Test Step 4.

• NOT OK - The voltage measurement is greater than 8.0 ± 0.3 VDC. The measurement is not correct. Proceed to Test Step 2.

Test Step 2. CHECK THE POWER SUPPLY AT THE ECM

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

2. At the J1 connector for the ECM, use a wire removal tool to remove contact J1-44 (wire X800-OR(Orange)) and contact J1-45 (wire C241-BK(Black)) from the J1 connector. The machine harness connector J1 remains connected to the Transmission ECM.

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

4. Use the multimeter probes in order to make contact on the connector pins. Measure the voltage at the pins of the Transmission ECM between the contact J1-44 and contact J1-45.

Expected Result:

The voltage measurement is 8.0 ± 0.3 VDC.

Results:

• OK - The voltage measurement is 8.0 ± 0.3 VDC. The voltage is correct. The ECM power supply is correct. Install the wires and sockets that were removed from the J1 connector back into the original locations. Proceed to Test Step 3.

• NOT OK - The voltage measurement is greater than 8.0 ± 0.3 VDC. The ECM power supply is not correct. The ECM has failed.

  Repair: Prior to replacing an ECM, always contact your dealership Technical Communicator 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

Test Step 3. CHECK FOR A SHORT CIRCUIT IN THE MACHINE HARNESS

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

2. Disconnect the machine harness connectors from the sensors in Illustration 1.

3. Disconnect the machine harness connectors J1 and J2 from the ECM.

4. At the J1 connector of the ECM, check the resistance from contact J1-44 (wire X800-OR(Orange)) to all the other connections of the +battery in the J1 and J2 harness connectors.

Expected Result:

Each resistance measurement is greater than 5000 ohms.

Results:

• OK - Each resistance measurement is greater than 5000 ohms. The supply circuit is not shorted to another circuit in the machine harness. Proceed to Test Step 4.

• NOT OK - One or more of the resistance measurements is less than 5000 ohms. There is a short in the machine harness.

  Repair: The power supply circuit is shorted to another circuit in the machine harness. Refer to the Electrical System Schematic for the machine. Examine the supply circuit in order to determine the location of the problem.

  For information on testing for short circuits and finding short circuits, refer to Testing and Adjusting, "Wiring Harness (Short Circuit) - Test". 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 and 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 securely 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: It is unlikely that the ECM has failed. 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