797 and 797B Off-Highway Truck/Tractors Braking System Caterpillar

Illustration 1	g00875930
Schematic of CAT Data Link

This diagnostic code is associated with the transmission ECM.

This diagnostic code is recorded when the brake/cooling ECM is unable to communicate with the transmission ECM through the CAT data link. There is no response from the ECM or the response is incorrect.

System Response:

This diagnostic code results in events that are logged against an ECM that can not be explained directly. The brake ECM cannot communicate with the transmission ECM or the ECM appears to communicate intermittently.

Test Step 1. VERIFY THE HARDWARE AND THE SOFTWARE PART NUMBERS.

1. Verify that the following information is correct:
   • The part number of the flash software for the transmission ECM

   • The part number of the transmission ECM

   • The part number of the flash software for the brake ECM

   • The part number of the brake ECM

   Note: Consult the Business Unit that produces the product for the correct part numbers of the flash software.

Expected Result:

All the part numbers are correct.

Results:

• OK - All the part numbers are correct. Proceed to Test Step 2.

• NOT OK - All the part numbers are NOT correct.

  Repair: The ECM has the wrong part number or the incorrect software is installed. Replace the ECM with a module that has the correct part number. Flash the correct software. See the Testing and Adjusting, "Electronic Control Module (ECM)-Flash Program" section of this manual.

  Stop.

Test Step 2. INSPECT THE HARNESS CONNECTIONS.

1. Turn the disconnect switch to the OFF position.

2. Inspect all harness connections that are related to the CAT data link. Make sure that the connectors are clean and tight.

3. Check the connectors for proper mating. Ensure that all the seals are present and in place.

4. Check the harness for signs of damage or abrasion.

5. Check the wires at the connector. Ensure that the wires are secured tightly into the connector. Take care not to pull the wire out of the connector.

6. Check the exposed wires at the connectors for nicks or signs of abrasion.

7. Check for moisture inside the connector.

8. Check the connectors for dirty contacts or corroded contacts.

9. Check each pin and each socket of the machine harness connectors. Ensure that the contacts are properly installed. The contacts should mate correctly when the two pieces of the connector are placed together.

Expected Result:

The machine harness connectors are tight and free of corrosion.

Results:

• OK - The machine harness connectors are tight and free of corrosion. Proceed to Test Step 3.

• NOT OK - The machine harness connectors are in need of repair.

  Repair: Repair the machine harness and/or the connector or replace the machine harness and/or the connector.

  Stop.

Test Step 3. CHECK FOR SHORTS TO GROUND

1. The disconnect switch remains in the OFF position.

2. Disconnect the machine harness from all electronic control modules that use the CATdata link.

3. At the machine harness for the brake ECM, measure the resistance between contacts J1-8 (wire 893-GN) and J1-7 (wire 892-BR) of the CAT data link and frame ground.

Expected Result:

The resistance is greater than 5000 Ohms.

Results:

• OK - The resistance is greater than 5000 Ohms. The harness circuit resistance is correct. Proceed to Test Step 4.

• NOT OK - The resistance is less than 5000 Ohms. The machine harness has failed.

  Repair: There is a short between frame ground and the CAT data link circuit in the machine harness. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 4. CHECK THE MACHINE HARNESS FOR A SHORT TO THE +BATTERY CIRCUIT.

1. The disconnect switch remains in the OFF position.

2. All related electronic control modules remain disconnected from the machine harness.

3. At the machine harness connector for the brake ECM, perform the checks that are listed here:
   • Measure the resistance between the connector contact J2-1 and connector contact J1-8 (wire 893-GN).

   • Measure the resistance between connector contact J2-1 and connector contact J1-7(wire 892-BR).

Expected Result:

The resistance is greater than 5000 Ohms.

Results:

• OK - The harness circuit resistance is correct. Proceed to Test Step 5.

• NOT OK - The resistance is less than 5000 Ohms. The machine harness has failed.

  Repair: There is a short between the +battery circuit and the circuits of the CAT data link circuit in the machine harness. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 5. CHECK FOR OPEN HARNESS

1. The disconnect switch remains in the OFF position.

2. All related electronic control modules remain disconnected from the machine harness.

3. Check the continuity of the CAT data link circuit in the machine harness:
   • Measure the resistance between connector contact J1-8 (wire 893-GN) of the brake ECM and connector contact J1-8 (wire 893-GN) of the transmission ECM.

   • Measure the resistance between connector contact J1-7 (wire 892-BR) of the brake ECM and connector contact J1-7 (wire 892-BR) of the transmission ECM.

Expected Result:

The resistance measures less than 5 Ohms.

Results:

• OK - The resistance is less than 5 Ohms. The CAT data link circuit in the machine harness is correct. Proceed to Test Step 6.

• NOT OK - The resistance is greater than 5 Ohms. The machine harness has failed.

  Repair: The CAT data link circuit is open in the machine harness. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 6. CHECK FOR ADDITIONAL DIAGNOSTIC CODES FOR THE OTHER ELECTRONIC CONTROL MODULES.

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

2. One at a time, reconnect the electronic control modules that use the CAT data link.

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

4. After each of the electronic control modules has been reconnected, check the Event List for diagnostic codes that are logged against the electronic control module.

Expected Result:

Diagnostic codes are not present for the other electronic control modules in the event list.

Results:

• OK - Diagnostic codes are not present for the other electronic control modules in the event list.

  Repair: The brake ECM has failed. It is unlikely that the ECM has failed. Exit this procedure. Perform this procedure again. If the failure is not found, check the +battery contacts and ground contacts of the ECM. If these contacts are correct, replace the ECM.

  Stop.

• NOT OK - Diagnostic codes are present for the other electronic control modules (ECM) in the event list.

  Repair: The transmission ECM has failed. It is unlikely that the ECM has failed. Exit this procedure. Perform this procedure again. If the failure is not found, replace the ECM. See the Testing and Adjusting, "Module - Replace" section of this manual.

  Stop.