3126B Marine Engines Caterpillar

Use this procedure to troubleshoot the system only when there is an active diagnostic code or when a diagnostic code can easily be activated. This procedure covers open circuit diagnostic codes and short circuit diagnostic codes that are associated with the following sensors:

• Coolant temperature sensor

• Engine oil temperature sensor

• Fuel temperature sensor

• Inlet manifold temperature sensor

Note: This application may be equipped with a transmission oil temperature sensor that requires a different troubleshooting procedure. Refer to Troubleshooting, "Transmission Oil Temperature Sensor Open or Short Circuit - Test" for the proper procedure.

The troubleshooting procedures for the diagnostic codes of each temperature sensor are identical. The temperature sensors are passive sensors that have two terminals. The temperature sensors do not require supply voltage from the Electronic Control Module (ECM).

Illustration 1	g01051650
Schematic

Illustration 2	g01051662
P2 ECM connector

Test Step 1. Verify all Active Diagnostic Codes

1. Connect the electronic service tool to the service tool connector.

2. Turn the keyswitch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

3. Monitor the "Active Diagnostic Codes" screen on the electronic service tool.

Expected Result:

There is an active diagnostic code for one or more of the temperature sensors.

Results:

• Yes - There is an active diagnostic code for one or more of the temperature sensors. Proceed to Test Step 2.

• No - There are no active diagnostic codes for the temperature sensors.

  Repair: If there are logged diagnostic codes for one or more of the temperature sensors and the engine is not running properly, refer to Troubleshooting, "Troubleshooting without a Diagnostic Code". If the engine is running properly at this time, an intermittent condition may be causing the logged codes. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  Stop.

Test Step 2. Inspect Electrical Connectors and Wiring

1. Turn the keyswitch to the OFF/RESET position.

2. Thoroughly inspect the J2/P2 ECM connector, the suspect sensor connector, and any other connectors in the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the sensor connector and the ECM connector that are associated with the active diagnostic code.

4. Verify that the latch tab of the connector is properly latched.

5. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

6. Check the harness and wiring for abrasions and for pinch points from the sensor to the ECM.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - Proceed to Test Step 3.

• Not OK -

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  Stop.

Test Step 3. Verify that the Diagnostic Code is Still Active

1. Turn the keyswitch to the ON position. Wait at least 15 seconds for activation of the diagnostic code.

2. Access the "Active Diagnostic Codes" screen on the electronic service tool and check for active diagnostic codes.

3. Determine if the problem is related to an open circuit diagnostic code 03 or a short circuit diagnostic code 04.

Expected Result:

A short circuit diagnostic code 04 or an open circuit diagnostic code 03 is active.

Results:

• Short Circuit - A short circuit diagnostic code 04 is active at this time. Proceed to Test Step 4.

• Open Circuit - An open circuit diagnostic code 03 is active at this time. Proceed to Test Step 5.

• No Active Diagnostic Codes - The problem seems to be resolved.

  Repair: Carefully reinspect the connectors and wiring. Refer to Troubleshooting, "Electrical Connectors - Inspect" for additional information.

  Stop.

Test Step 4. Disconnect the Sensor in Order to Create an Open Circuit

1. Turn the keyswitch to the OFF/RESET position.

2. Disconnect the connector to the sensor with the short circuit diagnostic code 04.

3. Turn the keyswitch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

4. Access the "Active Diagnostic Codes" screen on the electronic service tool and check for an active open circuit diagnostic code 03 for the suspect sensor.

5. Turn the keyswitch to the OFF/RESET position.

Expected Result:

An open circuit diagnostic code 03 is now active for the disconnected sensor.

Results:

• OK - A short circuit diagnostic code 04 was active before disconnecting the sensor. An open circuit diagnostic code 03 became active after disconnecting the sensor.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Check for a short circuit diagnostic code 04 while the new sensor is connected. If the short circuit diagnostic code 04 is not present, permanently install a new sensor. Clear any logged diagnostic codes.Verify that the repair eliminates the problem.

  Stop.

• Not OK - The short circuit diagnostic code 04 is present. There is probably a short circuit between the sensor harness connector and the ECM. Disconnect the sensor. Proceed to Test Step 6.

Test Step 5. Short the Sensor Connector

1. Turn the keyswitch to the OFF/RESET position.

2. Unplug the suspect sensor.

3. Install a jumper wire with Deutsch sockets on each end between the terminals on the plug for the suspect sensor.

4. Turn the keyswitch to the ON position.

5. Wait at least 15 seconds for activation of the short circuit diagnostic code 04.

   Note: Monitor the "Active Diagnostic Codes" screen on the electronic service tool before installing the jumper wire and after installing the jumper wire.

6. Remove the jumper wire.

7. Turn the keyswitch to the OFF/RESET position.

Expected Result:

A short circuit diagnostic code 04 is active when the jumper wire is installed. An open circuit diagnostic code 03 is active when the jumper wire is removed.

Results:

• OK - The engine harness and the ECM are okay.

  Repair: Perform the following repair:

  1. Temporarily reconnect the suspect sensor.

  2. If the diagnostic code 03 is active, replace the sensor.

  3. Verify that the repair eliminates the problem.

  4. Clear all logged diagnostic codes.

  Stop.

• Not OK - The open circuit diagnostic code 03 remains active with the jumper in place. There appears to be an open circuit between the ECM and the sensor. Proceed to Test Step6.

Test Step 6. Check the Operation of the ECM by Creating Open and Short Circuits at the ECM Connector

1. Check the operation of the ECM by creating an open at the ECM.

   1. Turn the keyswitch to the OFF/RESET position.

   2. Disconnect the P2 ECM connector. Thoroughly inspect both halves of the connector for signs of corrosion and/or moisture.

   3. Remove the signal wire and the return wire for the suspect sensor from the P2 ECM connector. Reconnect the P2 connector.

      Note: Active open circuit diagnostic codes 03 will be generated for any other temperature sensors that share the return for the suspect sensor.

   4. Turn the keyswitch to the ON position. Monitor the "Active Diagnostic Code" screen on the electronic service tool. Wait at least 15 seconds for activation of the code.

   5. Turn the keyswitch to the OFF/RESET position.

2. Check the operation of the ECM by creating a short at the ECM.

   1. Install a jumper wire with Deutsch sockets on each end between the terminal for the suspect sensor signal and the return for the suspect sensor.

   2. Turn the keyswitch to the ON.

   3. Monitor the "Active Diagnostic Code" screen on the electronic service tool. Wait at least 15 seconds for activation of the code.

   4. Turn the keyswitch to the OFF/RESET position.

   5. Remove the wire jumper and reconnect ECM connector J2/P2.

Expected Result:

An open circuit diagnostic code 03 is active when the sensor wires are removed from the ECM connector. A short circuit diagnostic code 04 is active when the jumper wire is installed across the wires for the sensor.

Results:

• OK - The ECM is working properly. The problem is in the wiring between the ECM and the suspect sensor.

  Repair: If the code is active for more than one sensor, the problem is most likely in the return wire for the sensor. Repair the return wire for the sensor.If the code is active for one sensor, the problem is most likely in the signal wire for the sensor. Repair the signal wire for the sensor.

  Stop.

• Not OK - One of the following conditions exists: The open circuit diagnostic code 03 is not active when the harness is disconnected. The short circuit diagnostic code 04 is not active when the jumper wire is installed.

  Repair: Perform the following repair:

  1. Temporarily connect a spare ECM.

  2. Remove all jumper wires and reconnect all connectors and wires.

  3. Recheck the system for active diagnostic codes.

  4. Repeat this test step.

  5. If the problem is resolved with the spare ECM, reconnect the suspect ECM.

  6. If the problem returns with the suspect ECM, replace the ECM.

  7. Verify that the repair eliminates the problem.

  Stop.