725, 730, 735, 740 and 740 EJECTOR Articulated Trucks Power Train Electronic Control System Caterpillar

Illustration 1	g00756754
Schematic of the CAT Data Link Circuit

This failure results in events that are logged against an ECM that can not be explained. The Transmission/Chassis ECM cannot communicate with the Engine ECM or the ECM appears to work intermittently.

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

1. Verify that the following information is correct:
   • The part number for the configuration software of the Transmission/Chassis ECM

   • The part number of the "engine ECM flash software"

   • The part number of the Transmission/Chassis ECM

   • The part number of the engine ECM

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

Expected Result:

All part numbers are correct.

Results:

• OK - All part numbers are correct. Proceed to test step 2.

• NOT OK - All part numbers are NOT correct. The part number of the Transmission/Chassis ECM may be incorrect. The part number of the Engine ECM may be incorrect. The incorrect configuration software may also be installed.

  Repair: Replace the incorrect ECM with an ECM that has the correct part number. Flash the correct configuration software. See Testing and Adjusting, "Electronic Control Module (ECM) - Flash Program".

  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.

4. Check the wires at the connector.

5. Check each wire for nicks or signs of abrasion in the insulation.

6. Check for moisture at the connector.

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

8. Check each pin and each socket of the machine harness connectors.

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 or replace the machine harness.

  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 Transmission/Chassis ECM, measure the resistance between frame ground and connector contacts J1-8 (wire 893-GN) and J1-7 (wire 892-BR) of the CAT data link circuit.

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 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 Transmission/Chassis ECM, perform the checks that are listed here:
   • Measure the resistance between the connector contact J2-1 (wire 126-RD) and connector contact J1-8 (wire 893-GN).

   • Measure the resistance between connector contact J2-1 (wire 126-RD) 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 CAT data link circuit in the machine harness. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 5. CHECK FOR A 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 Transmission/Chassis ECM and connector contact J1-8 (wire 893-GN) of the engine ECM.

   • Measure the resistance between connector contact J1-7 (wire 892-BR) of the Transmission/Chassis ECM and connector contact J1-9 (wire 892-BR) of the engine 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. Reconnect all the electronic control modules that use the CAT data link.

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

3. 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 (ECM) in the event list.

Results:

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

  Repair: The engine 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.

  Stop.

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

  Repair: The Transmission/Chassis 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, "Electronic Control Module (ECM) - Replace".

  Stop.