C15 On-highway Engines Caterpillar

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

• Intake manifold air temperature sensor

• Coolant temperature sensor

• Ambient air temperature sensor

• Fuel temperature sensor

Note: The ambient temperature sensor is optional equipment.

This procedure covers the following diagnostic codes:

• 105-03 Intake Manifold Air Temperature voltage high

• 105-04 Intake Manifold Air Temperature voltage low

• 110-03 Coolant Temperature voltage high

• 110-04 Coolant Temperature voltage low

• 171-03 Ambient Air Temperature voltage high

• 171-04 Ambient Air Temperature voltage low

• 174-03 Fuel Temperature voltage high

• 174-04 Fuel Temperature voltage low

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 Engine 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	g01099399
Schematic for engine temperature sensors

Illustration 2	g01099400
P2 ECM connector (P2-13) Engine coolant temperature (P2-30) Common for the engine temperature sensors (P2-56) Intake manifold air temperature (P2-62) Fuel temperature

Illustration 3	g01099401
P1 ECM connector (P1-18) Sensor common #1 (P1-26) Ambient air temperature sensor

Illustration 4	g01104079
Sensor locations (1) Fuel temperature sensor (2) Intake manifold air temperature sensor

Illustration 5	g01104077
Sensor locations (3) Coolant temperature sensor

Test Step 1. INSPECT ELECTRICAL CONNECTORS AND WIRING

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the J2/P2 ECM connector, the J1/P1 ECM connector, and the suspect sensor connector. 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 - 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 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 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. Determine if the problem is related to an open circuit diagnostic code 03 or a short circuit diagnostic code 04.

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic 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 - A short circuit diagnostic code 04 is active at this time. Proceed to Test Step 3.

• Not OK - An open circuit diagnostic code 03 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 harness at the sensor connector.

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 open circuit diagnostic code 03 for the suspect sensor.

5. Turn the keyswitch to the OFF position.

Expected Result:

An open circuit diagnostic code 03 is now active for the suspect 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. 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 short circuit diagnostic code 04 is still present. The short circuit is between the sensor harness connector and the ECM. 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 (sensor common) at the sensor 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 suspect sensor connector.

  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. 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 ECM connectors P2 and ECM connector P1.

3. Measure the resistance between the terminal for the sensor signal wire at the ECM and every terminal on ECM connector P1 and ECM connector P2.

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

5. Turn the keyswitch to the OFF position.

6. Reconnect ECM connector P1 and ECM connector P2.

Expected Result:

The resistance is greater than 20,000 Ohms.

Results:

• OK - The resistance is greater than 20,000 Ohms. Proceed to Test Step 6.

• Not OK - The resistance is less than 20,000 Ohms.

  Repair: The resistance measurement indicates a low resistance between two or more wires. Repair the connectors or wiring and/or replace the connectors or wiring.

  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 terminal 1 and terminal 2 on the connector for the suspect sensor. Connect the jumper on the harness side of the connector.

3. Turn the keyswitch to the ON position.

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

   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.

6. Turn the keyswitch to the OFF 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: 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 open circuit diagnostic code 03 remains active with the jumper in place. The open circuit is between the ECM and the sensor connector. 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 at the ECM.

   1. Remove the signal wire for the suspect sensor from the P2 ECM connector or the P1 ECM connector.

   2. Remove the sensor return for the suspect sensor from the P2 ECM connector or the P1 ECM connector.

      Note: Disconnecting the sensor return from the ECM will generate an open circuit diagnostic code for all sensors that are connected to the sensor return. Troubleshoot the original diagnostic code. Delete 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 open circuit diagnostic code 03 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 and the sensor return.

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

      A short circuit diagnostic code (04) should be active when the wire jumper is installed.

   3. Remove the wire jumper and reconnect all wires.

Expected Result:

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

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 open circuit diagnostic code 03 is not active when the sensor signal wire is disconnected. The short circuit diagnostic code 04 is not active when the wire jumper is installed.

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

  STOP