C7 and C9 Marine Engines Caterpillar

Use this procedure to troubleshoot any suspect problems with the following sensors:

• Engine coolant temperature sensor

• Inlet manifold temperature sensor

• Fuel temperature sensor

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

This procedure covers the following diagnostic codes:

• 105-03 Inlet Manifold Temp Sensor open/short to +batt

• 105-04 Inlet Manifold Temp Sensor short to ground

• 110-03 Engine Coolant Temperature open/short to +batt

• 110-04 Engine Coolant Temperature short to ground

• 174-03 Fuel Temperature open/short to +batt

• 174-04 Fuel Temperature short to ground

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).

Pull-up Voltage

The ECM continuously outputs a pull-up voltage on the circuit for the sensor signal wire. The ECM uses this pull-up voltage in order to detect an open in the signal circuit. When the ECM detects the presence of a voltage that is above a threshold on the signal circuit, the ECM will generate an open circuit diagnostic code (03) for the sensor.

If the sensor is disconnected at the sensor connector, the presence of pull-up voltage at the sensor connector indicates that the wires from the sensor connector to the ECM are not open or shorted to ground. If the sensor is disconnected at the sensor connector, the absence of pull-up voltage at the sensor connector indicates an open in the signal wire or a short to ground. If the sensor is disconnected at the sensor connector and the voltage at the sensor connector is different from pull-up voltage, the signal wire is shorted to another wire in the harness.

Illustration 1	g01200240
Schematic for the engine temperature sensors

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove the electrical power from the ECM.

Show/hide table



Illustration 2	g01153097
Typical left side engine view (1) Engine coolant temperature sensor (2) Fuel temperature sensor (3) Intake manifold air temperature sensor (4) J2/P2 ECM connector

2. Inspect the connectors for sensors (1), (2), and (3). Also, thoroughly inspect connectors (4). Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

Show/hide table



Illustration 3	g01229400
P2 terminals that are associated with the engine temperature sensors (P2-13) Engine coolant temperature (P2-30) Return (P2-56) Intake manifold air temperature (P2-62) Fuel temperature

Show/hide table



Illustration 4	g01155187
Harness connector for the temperature sensors (1) Signal (2) Return

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the temperature sensors.

4. Check the allen head screw on each ECM connector for the proper torque. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

5. Check the harness and wiring for abrasions and for pinch points from each 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 - The connectors and wiring appear to be OK. Proceed to Test Step 2.

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. 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 2. Check for Active Diagnostic Codes

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector.

2. Restore the electrical power to the ECM.

3. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

4. Look for a 03 diagnostic code or a 04 diagnostic code.

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active. The problem appears to be resolved.

  Repair: The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - A 04 diagnostic code is active at this time. Proceed to Test Step 3.

• Not OK - A 03 diagnostic code is active at this time. Proceed to Test Step 4.

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

1. Remove the electrical power from the ECM.

2. Disconnect the suspect sensor from the engine harness.

3. Restore electrical power to the engine ECM. Wait at least 30 seconds for activation of the diagnostic codes.

4. Access the "Active Diagnostic Codes" screen on Cat ET and check for an active 03 diagnostic code for the suspect sensor.

5. Remove the electrical power from the ECM.

Expected Result:

A 03 diagnostic code is now active for the suspect sensor.

Results:

• OK - A 04 diagnostic code was active before disconnecting the sensor. A 03 diagnostic code became active after the sensor was disconnected. There may be a problem with the sensor.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the new sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes. Verify that the repair eliminates the problem.

  STOP

• Not OK - The 04 diagnostic code is still present. Leave the sensor disconnected. There may be a problem with the harness or with the ECM. Proceed to Test Step 5.

Test Step 4. Create a Short at the Sensor Connector

1. Disconnect the suspect sensor from the sensor connector.

2. Fabricate a jumper wire that can be used to create a short between terminal 1 (signal) and terminal 2 (sensor return) at the suspect sensor's connector. Crimp connector pins to each end of the jumper wire.

3. Install the jumper into the harness side of the sensor connector.

4. Restore the electrical power to the ECM.

5. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active 04 diagnostic code for the suspect sensor.

6. Remove the electrical power from the ECM.

Expected Result:

A 04 diagnostic code is now active for the suspect sensor.

Results:

• OK - A 03 diagnostic code was active before creating the short at the sensor connector. A 04 diagnostic code became active after creating the short at the sensor connector.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the new sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - A 03 diagnostic code is still active for the suspect sensors. Proceed to Test Step 5.

Test Step 5. Check the Operation of the ECM

1. Remove the electrical power from the ECM.

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

   1. Disconnect the P2 ECM connector.

   2. Fabricate a jumper wire that is long enough to reach from a terminal at the ECM connector to the engine ground stud. Crimp a connector socket to one end of the jumper wire.

   3. Remove the signal wire for the suspect sensor from the P2 ECM connector. Install the jumper wire into the terminal location for the signal wire of the suspect sensor.

   4. Connect the ECM connectors.

   5. Restore the electrical power to the ECM.

   6. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code.

      An open circuit diagnostic code (03) will be active for the suspect sensor.

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

   1. Short the jumper wire that is installed into the P2 ECM connector to engine ground.

   2. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code.

      A short circuit diagnostic code (04) will be active for the suspect sensor.

   3. Remove the electrical power from the ECM.

4. Remove the wire jumper. Reconnect all wires and connectors.

Expected Result:

A 03 diagnostic code is active when the sensor signal wire is open the ECM connector. A 04 diagnostic code is active when the jumper wire is shorted to engine ground.

Results:

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

  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 or replace the harness.If the code is only active for one sensor, the problem is most likely in the signal wire for the sensor. Repair the signal wire for the sensor. Verify that the repair eliminates the problem.

  STOP

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

  Repair: Replace the ECM. Refer to electronic troubleshooting Troubleshooting, "Replacing the ECM". Verify that the original problem is resolved.

  STOP