3126B Petroleum Engine Caterpillar

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

• Coolant temperature sensor

• Intake manifold air temperature sensor

• Engine oil 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

• 175-03 Engine Oil Temperature open/short to +batt

• 175-04 Engine Oil 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 wire, the ECM will generate a -03 diagnostic code.

If the sensor is disconnected at the sensor connector, the presence of pull-up voltage at the sensor connector indicates that the signal wire and the return wire from the sensor connector to the ECM are good.

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, an open in the return wire, or a short to ground.

If the sensor is disconnected at the sensor connector and the voltage on the signal wire at the sensor connector is different from pull-up voltage, the signal wire is shorted to another wire in the harness.

Show/hide table

The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere.

Test Step 1. Inspect the Electrical Connectors and the Wiring

Show/hide table



Illustration 1	g01069296
Schematic

1. Turn the keyswitch to the OFF position.

Show/hide table



Illustration 2	g01129440
Left side view (1) Engine coolant temperature sensor (2) Intake manifold air temperature sensor (3) Engine oil temperature sensor (4) ECM (5) J2/P2 ECM connector

2. Thoroughly inspect connector (5). Inspect the connectors for sensors (1), (2), and (3). Refer to Troubleshooting, "Electrical Connectors - Inspect".

Show/hide table



Illustration 3	g01129493
P2 terminations for the engine temperature sensors (P2-18) Sensor return (P2-32) Engine coolant temperature (P2-34) Engine oil temperature (P2-35) Intake manifold air temperature

Show/hide table



Illustration 4	g01120369
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 the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque.

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 are 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. Turn the keyswitch to the ON position.

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

   Note: Wait at least 15 seconds in order for the diagnostic codes to become active.

4. Look for an active -03 diagnostic code or an active -04 diagnostic code.

Expected Result:

No -03 or -04 diagnostic codes are active.

Results:

• OK - No -03 or -04 codes are active.

  Repair: 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 - An -04 diagnostic code is active at this time. Proceed to Test Step 3.

• Not OK - An -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. Turn the keyswitch to the OFF position.

2. Disconnect the suspect sensor from the engine harness.

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 Cat ET and check for an active -03 diagnostic code for the suspect sensor.

5. Turn the keyswitch to the OFF position.

Expected Result:

An -03 diagnostic code is now active for the suspect sensor.

Results:

• OK - An 04 diagnostic code was active before disconnecting the sensor. An 03 diagnostic code became active after the sensor was disconnected.

  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 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. Proceed to Test Step 7.

Test Step 4. Check the Pull-up Voltage at the Sensor Connector

1. Disconnect the suspect sensor at the sensor connector.

2. Turn the keyswitch to the ON position.

3. Measure the voltage between terminal 1 (signal) and terminal 2 (return) at the harness connector.

4. Turn the keyswitch to the OFF position.

Expected Result:

The voltage is 5.5 ± 0.5 VDC.

Results:

• OK - The voltage is 5.5 ± 0.5 VDC. The correct pull-up voltage is present at the harness connector for the suspect sensor.

  Repair: The open circuit is in the sensor or the wire between the sensor and the sensor connector. Replace the sensor. Do not install the sensor in the engine. Verify that no diagnostic codes are active for the suspect sensor before permanently installing the sensor.

  STOP

• Not OK - The voltage is not 5.5 ± 0.5 VDC. There is a short circuit to another wire in the wiring harness. Proceed to Test Step 5.

Test Step 5. Check the Signal Wire for a Short Circuit

1. Turn the keyswitch to the OFF position.

2. Disconnect the P2 ECM connector.

3. Measure the resistance between the terminal for the suspect sensor's signal wire at the ECM connector and all of the remaining terminals on the P2 connector.

4. Measure the resistance between the terminal for the suspect sensor's signal wire at the ECM connector and the engine ground.

5. Connect the J2/P2 ECM connector.

Expected Result:

Each check of the resistance indicates an open circuit.

Results:

• OK - Each check of the resistance indicates an open circuit. Proceed to Test Step 6.

• Not OK - At least one check of the resistance does not indicate an open circuit. There is a short circuit in the wiring. There may be a problem with a connector.

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Verify that the original problem is resolved.

  STOP

Test Step 6. Create a Short at the Suspect Sensor Connector

1. Turn the keyswitch to the OFF position.

2. Install a jumper wire between terminals 1 and 2 on the harness connector for the suspect sensor.

3. Turn the keyswitch to the ON position.

4. Wait at least 15 seconds for activation of the 04 diagnostic code.

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

5. Remove the jumper wire. Check for an -04 diagnostic code again.

6. Turn the keyswitch to the OFF position.

Expected Result:

An -04 diagnostic code is active when the jumper wire is installed. An -03 diagnostic code is active when the jumper wire is removed.

Results:

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

  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 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. Proceed to Test Step 7.

Test Step 7. Check the Operation of the ECM

1. Turn the keyswitch to the OFF position.

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

   1. Remove the signal wire for the suspect sensor from the appropriate ECM connector.

   2. Remove P2-18 sensor return from the ECM connector.

      Note: Disconnecting the return wire from the ECM will generate an 03 diagnostic code for all sensors that are connected to the return wire. Troubleshoot the original diagnostic code. Clear the logged diagnostic codes when you are finished.

   3. Turn the keyswitch to the ON position. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 15 seconds for activation of the code.

      An -03 diagnostic code should be active for the suspect sensor.

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

   1. Install a wire jumper between the terminals for the sensor signal wire and the return wire.

   2. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 15 seconds for activation of the code.

      An -04 diagnostic code should be active when the wire jumper is installed.

   3. Remove the wire jumper. Return all wiring to the original configuration.

Expected Result:

An -03 diagnostic code is active when the sensor signal wire is removed from the ECM connector. An -04 diagnostic code is active when the signal wire is connected to the return wire.

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.

  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 Troubleshooting, "Replacing the ECM". Verify that the original problem is resolved.

  STOP