3126B Generator Set Engine Caterpillar

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

• Engine 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 Temperature open/short to +batt

• 172-04 Intake Manifold Air Temperature 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.

Illustration 1	g01194226
Schematic for the engine temperature sensors

Illustration 2	g01194233
P2 terminals that are associated with the engine temperature sensors (P2-18) Sensor return (P2-32) Engine coolant temperature (P2-34) Engine oil temperature (P2-35) Intake manifold air temperature

Illustration 3	g01155187
Harness connector for the temperature sensors (Terminal 1) Signal (Terminal 2) Return

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the engine ECM.

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Illustration 4	g01194229
Left side engine view (1) Engine coolant temperature sensor (2) Engine oil temperature sensor (3) Intake manifold air temperature sensor

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

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

2. Restore electrical power to the engine 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 Troubleshooting, "Electrical Connectors - Inspect" for additional information.

  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 electrical power from the engine ECM.

2. Disconnect the suspect sensor from the engine harness.

3. Restore electrical power to the engine ECM.

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

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

5. Remove electrical power from the engine 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. Proceed to Test Step 5.

Test Step 4. Create a Short at the Sensor Connector

1. Remove electrical power from the engine ECM.

2. Disconnect the suspect sensor at the sensor connector.

3. 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.

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

5. Restore electrical power to the engine ECM.

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

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

7. Remove electrical power from the engine 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 electrical power from the engine ECM.

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

   1. Disconnect the ECM connector for the suspect sensor.

   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 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 electrical power to the engine 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 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 electrical power from the engine 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. 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 Troubleshooting, "Replacing the ECM". Verify that the original problem is resolved.

  STOP