3176C Engines for Caterpillar Built Machines Caterpillar

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

• Engine coolant temperature sensor

• Fuel temperature sensor

• Intake manifold air temperature sensor

This procedure covers the following diagnostic codes:

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

• 110-04 Engine Coolant Temperature short to ground

• 172-03 Intake Manifold Air Temp open/short to +batt

• 172-04 Intake Manifold Air Temp 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 a problem 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 OK. If the sensor is disconnected at the sensor connector, the absence of pull-up voltage at the sensor connector indicates a problem in the signal wire. 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	g01276413
Schematic for the engine temperature sensors

Illustration 2	g01285043
(1) Engine coolant temperature sensor (2) Intake manifold air temperature sensor (3) Fuel temperature sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.

2. Thoroughly inspect all electrical connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 3	g01285082
(4) J2/P2ECM connector

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Illustration 4	g01285091
P2 terminals that are associated with the engine temperature sensors (P2-32) Engine coolant temperature (P2-18) Sensor return (P2-35) Intake manifold air temperature (P2-33) Fuel temperature

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Illustration 5	g01155187
Harness connector for the temperature sensors (1) Sensor signal (2) Sensor return

3. Perform a 45 N (10 lb) pull test on each of the wires at the connectors for the temperature sensors.

4. Check the allen head screw on each ECM connector and the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

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 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 2. Check for Active Diagnostic Codes

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

2. Restore 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. Check for an active 03 or 04 diagnostic code.

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active.

  Repair: The problem appears to be resolved. The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. Refer to Troubleshooting, "Electrical Connectors - Inspect" for additional information.

  STOP

• Not OK - A 03 diagnostic code is active at this time. The ECM detects an open circuit condition. Proceed to Test Step 4.

• Not OK - A 04 diagnostic code is active at this time. The ECM detects a short circuit condition. Proceed to Test Step 3.

Test Step 3. Create an Open Circuit by Disconnecting the Sensor Connector

1. Remove electrical power from the ECM.

2. Disconnect the suspect sensor from the harness at the sensor connector.

3. Restore electrical power to the ECM.

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

   Note: Wait at least 30 seconds for activation of the diagnostic codes.

5. Remove electrical power from the ECM.

Expected Result:

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

Results:

• OK - A 03 diagnostic code became active after the sensor was disconnected.

  Repair: There may be a problem with the sensor. 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 sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - The 04 diagnostic code is still present while the sensor is disconnected from the harness. The sensor is OK. There is a problem in the harness between the ECM and the sensor connector. There may be a problem with the ECM. Leave the suspect sensor disconnected. Proceed to Test Step 5.

Test Step 4. Short the Suspect Sensor at the Harness Connector

1. Remove electrical power from the ECM.

2. Disconnect the suspect sensor at the harness connector.

3. Fabricate a jumper wire that is long enough to short circuit the two terminals at the connector for the suspect sensor. Crimp connector pins to each end of the jumper wire.

4. Install the jumper wire between terminal 1 (sensor signal) and terminal 2 (sensor return) on the harness side of the suspect sensor's connector.

5. Restore electrical power to the ECM.

6. Monitor the "Active Diagnostic Codes" screen on Cat ET after installing the jumper wire. Check for an active 04 diagnostic code.

   Note: Wait at least 30 seconds for activation of the 04 diagnostic code.

7. Remove electrical power from the ECM.

Expected Result:

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

Results:

• OK - A 04 diagnostic code is active when the jumper wire is installed.

  Repair: There may be a problem with the sensor. 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 sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - The 03 diagnostic code remains active with the jumper in place. There is an open circuit between the ECM and the sensor connector. There may be a problem with the ECM. Proceed to Test Step 5.

Test Step 5. Check the Operation of the ECM

1. Remove electrical power from the ECM.

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

   1. Disconnect the appropriate ECM connector.

   2. Fabricate a jumper wire that is long enough to create a test circuit between the ECM connector and 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 appropriate ECM connector. Install the jumper wire into this terminal location.

   4. Connect the ECM connectors.

      Hold the loose end of the jumper wire away from any ground source in order to create an open circuit condition.

   5. Restore electrical power to the ECM.

   6. Monitor the "Active Diagnostic Code" screen on Cat ET. A 03 diagnostic code will become active for the suspect sensor.

      Note: Wait at least 30 seconds for activation of the code.

   7. Remove electrical power from the ECM.

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

   1. Connect the loose end of the jumper wire to the engine ground stud in order to create a short circuit condition.

   2. Restore electrical power to the ECM.

   3. Monitor the "Active Diagnostic Code" screen on Cat ET. A 04 diagnostic code will become active when the jumper wire is grounded.

      Note: Wait at least 30 seconds for activation of the code.

   4. Remove electrical power from the ECM.

4. Restore all wiring to the original configuration.

Expected Result:

A 03 diagnostic code is active when the jumper wire is open. A 04 diagnostic code becomes active when the jumper wire is shorted to the engine ground stud.

Results:

• OK - A 03 diagnostic code is active when the jumper wire is open. A 04 diagnostic code becomes active when the jumper wire is shorted to the engine ground stud.

  Repair: The ECM is working properly. The problem is in the wiring harness between the ECM and the sensor connector. Repair the harness and/or the connectors. Replace parts, if necessary.

  STOP

• Not OK - One of the following conditions exists: The 03 diagnostic code is not active when the jumper wire is open. The 04 diagnostic code is not active when the wire jumper is shorted to ground.

  Repair: There is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP