3512B Marine Auxiliary Engine Caterpillar

Use this procedure to troubleshoot thermocouples that have diagnostic codes which are active or easily repeated.

A thermocouple is installed into the exhaust port of each engine cylinder. A thermocouple is installed into each turbocharger in order to measure the outlet temperature. A thermocouple is installed into the air manifold in order to measure the engine outlet temperature.

The thermocouples do not require a supply voltage from the Integrated Temperature Sensing Module (ITSM). Each thermocouple has two wires. Each thermocouple develops a low voltage signal that is detected by the ITSM.

A 03 diagnostic code may be caused by a thermocouple wire that has a short circuit to a high voltage. A 03 diagnostic code may also occur if the thermocouple's voltage is above an acceptable range.

A 04 diagnostic code may be caused by a thermocouple wire that has a short circuit to a low voltage. A 04 diagnostic code may also occur if the thermocouple has a short to ground.

A diagnostic code is probably caused by a problem with a harness connector or a wiring problem. The next likely cause is a faulty thermocouple. The least likely cause is a problem with the ITSM.

This troubleshooting procedure may generate additional diagnostic codes. Stay aware of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.

Illustration 1	g00926402

Illustration 2	g00864501
(1) 54-pin connector for the ITSM (2) Connector for the thermocouple

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Turn the engine control switch to the OFF/RESET position.

2. Thoroughly inspect the connectors for the suspect thermocouple:
   • 54-pin connector for the ITSM

   • Connectors for the thermocouple

3. Check the harness and wiring for abrasion and pinch points from the suspect thermocouple to the ITSM.

Expected Result:

All of the connectors and terminals are connected properly. The connectors and the wiring are free of corrosion, abrasion and pinch points.

Results:

• OK - The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - The components are not in good condition and/or at least one connection is improper.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.

Test Step 2. Verify the Active Diagnostic Code

1. Turn the engine control switch to the STOP position.

2. Observe the "Active Diagnostic" screen on the electronic service tool. Wait at least 30 seconds so that any codes may become activated.

Expected Result:

None of the above codes are active.

Results:

• No active codes - The problem seems to be resolved. There are no active codes. The thermocouples are operating correctly at this time.

  Repair: The initial diagnostic code was probably caused by a poor electrical connection in one of the harness connectors. Resume normal operation.

  Stop.

• Active short to +batt (FMI 03) - There is an active short to +batt diagnostic code. Proceed to Test Step 3.

• Active short to ground (FMI 04) - There is an active short to ground diagnostic code. Proceed to Test Step 3.

• Active open circuit (FMI 05) - There is an active open circuit diagnostic code. Proceed to Test Step 4.

Test Step 3. Disconnect the Sensor in Order to Create an Open Circuit

1. Turn the engine control switch to the OFF/RESET position.

2. Disconnect the thermocouple that has the short circuit diagnostic code.

3. Turn the engine control switch to the STOP position.

4. Observe the "Active Diagnostic" screen on the Caterpillar Electronic Technician (ET). Wait at least 30 seconds so that any codes may become activated.

Expected Result:

An open circuit diagnostic code was generated for the suspect thermocouple.

Results:

• OK - Before the suspect thermocouple was disconnected, there was an active "short circuit" diagnostic code. After the thermocouple was disconnected, there was an active "open circuit" diagnostic code.

  Repair: Reconnect the thermocouple. If the active "short circuit" diagnostic code reoccurs, replace the thermocouple. Verify that the problem is resolved. Lubricate the threads of the new thermocouple with a nickel based, high temperature anti-seize compound. Tighten the new thermocouple to 25 ± 5 N·m (18 ± 4 lb ft).

  Stop.

• Not OK - Before the suspect thermocouple was disconnected, there was an active "short circuit" diagnostic code. After the thermocouple was disconnected, the active "short circuit" diagnostic code remained. Proceed to Test Step 5.

Test Step 4. Create a Short Circuit at the Connector for the Thermocouple

1. Turn the engine control switch to the STOP position.

2. Fabricate a jumper wire with the appropriate terminals on each end.

Note: Observe the "Active Diagnostic" screen on the Cat ET before installing the jumper wire and after installing the jumper wire.

3. Insert one end of the jumper wire into the positive socket of the harness connector for the suspect thermocouple. Connect the other end of the jumper wire to an acceptable engine ground. The jumper wire must remain connected in this manner for at least 30 seconds.

4. Insert one end of the jumper wire onto the negative socketof the harness connector for the suspect thermocouple. Connect the other end of the jumper wire to an acceptable engine ground. The jumper wire must remain connected in this manner for at least 30 seconds.

5. Remove the jumper wire from the engine harness. The jumper wire must be removed for at least 30 seconds.

Expected Result:

A "short circuit" diagnostic code becomes active when the jumper wire is connected to the engine harness for 30 seconds. An "open circuit" diagnostic code becomes active when the jumper wire is removed from the engine harness for 30 seconds.

Results:

• OK - A "short circuit" diagnostic code becomes active when the jumper wire is connected. An "open circuit" diagnostic code becomes active when the jumper wire is removed. The engine harness and the ITSM appear to be functioning properly.

  Repair: To verify that the thermocouple is faulty, reconnect the suspect thermocouple for at least 30 seconds. If the "open circuit" diagnostic code returns, replace the thermocouple. Verify that the new thermocouple does not create a diagnostic code. Lubricate the threads of the new thermocouple with a nickel based, high temperature anti-seize compound. Tighten the new thermocouple to 25 ± 5 N·m (18 ± 4 lb ft).

  Stop.

• Not OK - A "short circuit" diagnostic code is not active when the jumper wire is connected. The "open circuit" diagnostic code remains active at all times. The engine harness or the ITSM appears to have a problem. Proceed to Test Step 5.

Test Step 5. Check the Operation of the ITSM

1. Turn the engine control switch to the OFF/RESET position.

2. Disconnect the 54-pin connector from the ITSM.

Note: When the 54-pin connector is disconnected from the ITSM, numerous "open circuit" codes for the thermocouples will become active. Stay aware of the diagnostic code for the suspect thermocouple.

3. Turn the engine control switch to the STOP position. Wait at least 30 seconds so that any codes may become activated. "Open circuit" diagnostic codes for the thermocouples should activate. An "open circuit" diagnostic code for the suspect thermocouple should also be activated.

4. Turn the engine control switch to the OFF/RESET position.

5. Determine the positive terminal and the negative terminal for the suspect thermocouple.

6. Connect one end of a jumper wire to the appropriate positive pin on the 54-pin connector. Connect the other end of the jumper wire to an acceptable engine ground.

7. Turn the engine control switch to the STOP position. Wait at least 30 seconds so that any codes may become activated. A "short circuit" diagnostic code for the suspect sensor should be activated.

8. Turn the engine control switch to the OFF/RESET position.

9. Connect one end of the jumper wire to the appropriate negative pin on the 54-pin connector. Connect the other end of the jumper wire to an acceptable engine ground.

10. Turn the engine control switch to the STOP position. Wait at least 30 seconds so that any codes may become activated. A "short circuit" diagnostic code for the suspect sensor should be activated.

Expected Result:

An "open circuit" diagnostic code for the suspect thermocouple is activated when the 54-pin connector is disconnected from the ITSM. A "short circuit" diagnostic code is activated when the positive terminal is shorted to ground for at least 30 seconds. A "short circuit" diagnostic code is activated when the negative terminal is shorted to ground for at least 30 seconds.

Results:

• OK - Active diagnostic codes are created according to the above steps. The ITSM appears to be working properly. There appears to be a problem with the harness for the thermocouples.

  Repair: Repair any faulty wiring and/or connectors, when possible. Replace any faulty wiring and/or connectors, if necessary. Clear any diagnostic codes. Verify that the condition is resolved.

  Stop.

• Not OK - Active diagnostic codes are not created according to the above steps. The ITSM does not respond properly when the 54-pin connector is removed. The ITSM does not respond properly when the jumper wire is connected. The ITSM appears to be faulty.

  Repair: It is unlikely that there is a problem with the ITSM. Exit this procedure and perform the troubleshooting procedure again. If the problem is not resolved, perform the following procedure.Turn the engine control switch to the OFF/RESET position. Remove all jumper wires and reconnect all connectors.Temporarily connect a properly programmed ITSM.If the temporary ITSM operates correctly, disconnect the temporary ITSM and reconnect the original ITSM. Verify that the problem returns. If the temporary ITSM works and the original ITSM does not work, replace the faulty ITSM.

  Stop.