3126B and 3126E On-highway Engines Caterpillar

Use this procedure under the following situation:

Use this procedure to troubleshoot the system only when there is an active diagnostic code or when a diagnostic code can easily be activated. This procedure covers open circuit diagnostic codes and short circuit diagnostic codes that are associated with the following sensors:

• coolant temperature sensor

• air inlet temperature sensor

Use this procedure for the following Diagnostic Codes:

• 105-03 Inlet Manifold Temp Sensor Open Circuit (38)

• 105-04 Inlet Manifold Temp Sensor Short Circuit (38)

• 110-03 Coolant Temp Sensor Open Circuit (27)

• 110-04 Coolant Temp Sensor Short Circuit (27)

The following background information is related to this procedure:

The troubleshooting procedures for the diagnostic codes of each temperature sensor are identical. The temperature sensors are passive sensors that have two terminals. The passive sensors do not require supply voltage from the ECM. ECM connector J2/P2 terminal 18 is the common connection for the engine temperature sensors. The sensor common connection is shared between all of the temperature sensors. The common line is connected to each sensor connector terminal 2. Terminal 1 is the sensor output. The signal from terminal 1 of each sensor is supplied to the appropriate terminal at ECM connector J2/P2.

Illustration 1	g00767354

Illustration 2	g00724478
Schematic for engine temperature sensors

Test Step 1. Verify All Active Diagnostic Codes.

1. Connect an electronic service tool to the cab data link connector.

2. Turn the ignition key switch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

3. Verify if any of the following diagnostic codes are active:
   • 105-03 Inlet Manifold Air Temp Sensor Open Circuit (38)

   • 105-04 Inlet Manifold Air Temp Sensor Short Circuit (38)

   • 110-03 Coolant Temp Sensor Open Circuit (27)

   • 110-04 Coolant Temp Sensor Short Circuit (27)

Expected Result:

One or more of the preceding diagnostic codes are active.

Results:

• Yes - Proceed to Test Step 2.

• No -

  Repair: If the preceding codes are logged but not active and the engine is not running properly, refer to Troubleshooting, "Troubleshooting without a Diagnostic Code". If the engine is running properly at this time, an intermittent condition may be causing the logged codes. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

Test Step 2. Inspect Electrical Connectors and Wiring.

Illustration 3	g00724517

1. Thoroughly inspect ECM engine harness connector J2/P2 and the suspect sensor connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. 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.

   Refer to Illustration 3.

3. Verify that the latch tab of the connector is properly latched and that the latch tab of the connector has returned to the Fully Latching position.

4. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

5. Check the harness and wiring for abrasion and pinch points from the sensor to the ECM.

Expected Result:

All connectors, pins and sockets should be completely coupled and/or inserted and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK - Proceed to Test Step 3.

• Not OK -

  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 3. Verify that the Diagnostic Code is Still Active.

1. Turn the ignition key switch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

2. Access the "Active Diagnostic Code" screen of the electronic service tool. Check for active diagnostic codes.

3. Determine if the problem is related to an open circuit diagnostic code or a short circuit diagnostic code.

Expected Result:

A short circuit diagnostic code or an open circuit diagnostic code is active.

Results:

• Short Circuit - A short circuit diagnostic code is active at this time. Proceed to Test Step 4.

• Open Circuit - An open circuit diagnostic code is active at this time. Proceed to Test Step 5.

Test Step 4. Disconnect the Sensor in order to Create an Open Circuit.

1. Turn the ignition key switch to the OFF position.

2. Disconnect the sensor connector of the sensor with the short circuit diagnostic code.

3. Turn the ignition key switch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

4. Access the "Active Diagnostic Code" screen on the electronic service tool. Check for an active open circuit diagnostic code.

Expected Result:

An open circuit diagnostic code for the disconnected sensor is now active.

Results:

• OK - A short circuit diagnostic code was active before disconnecting the sensor. An open circuit diagnostic code became active after disconnecting the sensor. Proceed to test step 6.

• Not OK - There is a short circuit between the sensor harness connector and the ECM. Leave the sensor disconnected. Proceed to Test Step 7.

Test Step 5. Create a Short Circuit Between the Signal and the Common Terminals at the Sensor Connector.

1. Turn the ignition key switch to the ON position.

2. Fabricate a jumper wire150 mm (6 inch) long. Crimp a Deutsch terminal to both ends of the wire.

3. Monitor the "Active Diagnostic Code" screen before installing the jumper wire and after installing the jumper wire.

4. Install the jumper on the engine harness connector. Install one end of the jumper at the sensor signal (terminal 1). Install the other end of the jumper at the common connection for the engine temperature sensor (terminal 2). Wait at least 15 seconds for activation of the short circuit diagnostic code.

Expected Result:

A short circuit diagnostic code is active when the jumper is installed. An open circuit diagnostic code is active when the jumper is removed.

Results:

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

  Repair: Perform the following repair:

  1. Temporarily connect the suspect sensor.

  2. If the diagnostic code remains active, replace the sensor.

  3. Verify that the repair eliminates the problem.

  4. Clear all Logged diagnostic codes.

  STOP

• Not OK - The open circuit diagnostic code remains active with the jumper in place. The most probable location for the open is in the sensor common or the sensor signal wire in the engine harness between the ECM and the sensor. Remove the jumper. Proceed to Test Step 7.

Test Step 6. Determine if the Short Circuit is in the Connector or in the Sensor.

1. Thoroughly inspect the connector for moisture.

2. Inspect the seals and reconnect the sensor.

3. If the short circuit diagnostic code reappears, the sensor is the problem.

   1. Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine.

4. Check for a short circuit diagnostic code while the new sensor is connected to the harness.

Expected Result:

The short circuit diagnostic code is not present when a new sensor is connected.

Results:

• OK - Verify that the repair eliminates the problem. Clear the logged diagnostic codes.STOP

• Not OK -

  Repair: Repair the engine harness connector.

  STOP

Test Step 7. Check the Operation of the ECM by Creating Open and Short Circuits at the ECM Connector.

Illustration 4	g00767376
Engine harness connector

1. Turn the ignition key switch to the OFF position.

2. Disconnect the Connector for the ECM harness. Thoroughly inspect both halves of the connector for signs of corrosion or moisture.

3. Turn the ignition key switch to the ON position. Monitor the "Active Diagnostic Code" screen. Wait at least 15 seconds for activation of the code.

   An open circuit diagnostic code should be active for the suspect sensor.

   Note: When the engine harness is disconnected, all of the open circuit diagnostic codes for the pressure sensors will be active. This is normal. Disregard the diagnostic codes for the pressure sensors.

4. Turn the ignition key switch to the OFF position.

5. Fabricate a jumper wire 150 mm (6 inch) long. Crimp a Deutsch socket to both ends of the wire.

6. Install the jumper wire on the ECM pin terminal. Insert the jumper wire between the terminal for the suspect sensor signal and the common connection for the engine temperature sensor (terminal 18).

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

   Note: If access to the ECM connector is limited, it may be helpful to connect a breakout T to the ECM connector. This will allow the jumper wire to be inserted into the breakout T. Ensure that the jumper wire is inserted into the breakout T and that the full wiring harness is attached.

   Refer to Illustration 4 for the engine harness connector P2.

Expected Result:

Open circuit diagnostic codes are active when the jumper is removed. Short circuit diagnostic codes are active when the jumper is installed.

Results:

• OK - The ECM is working properly. Proceed to Test Step 8.

• Not OK - One of the following conditions exists: The open circuit diagnostic code is not active when the harness is disconnected. The short circuit diagnostic code is not active when the jumper wire is installed.

  Repair: Perform the following repair:

  1. Temporarily connect a test ECM.

  2. Remove all jumpers and replace all connectors.

  3. Recheck the system for active diagnostic codes.

  4. Repeat the test step.

  5. If the problem is resolved with the test ECM, reconnect the suspect ECM.

  6. If the problem returns with the suspect ECM, replace the ECM.

  7. Verify that the repair eliminates the problem.

  STOP

Test Step 8. Bypass the Harness Wiring Between the ECM and the Sensor Connector.

1. Turn the ignition key switch to the OFF position.

2. Disconnect the connector for the ECM harness, and the sensor connector.

3. Remove the sensor signal wire from the ECM connector.

4. Remove the signal wire (terminal 1) from the sensor connector on the engine harness.

5. Fabricate a jumper wire that is long enough to reach from the ECM to the sensor connector with Deutsch sockets on both ends.

6. Insert one end of the jumper into the ECM Connector. Insert the other end of the jumper into the sensor connector of the engine harness.

7. Reconnect the connector for the ECM harness and the sensor connector.

8. Turn the ignition key switch to the ON position.

9. Monitor the "Active Diagnostic Code" screen for either the open circuit diagnostic code for the sensor or the short circuit diagnostic code for the sensor.

Expected Result:

The diagnostic code disappears when the jumper is installed.

Results:

• OK - There is a problem in the wiring harness.

  Repair: Perform the following repair:

  1. Repair the faulty wiring harness or replace the faulty wiring harness.

  2. Clear all diagnostic codes.

  3. Verify that the repair eliminates the problem.

  STOP

• Not OK - Restart this procedure and carefully perform each step.STOP