3406E, C-10, C-12, C-15, C-16 and C-18 On-highway Engines Caterpillar

The troubleshooting procedures for the diagnostic codes of each pressure sensor are identical. The Engine Control Module (ECM) sends a 5 Volt supply to terminal A of each sensor. The sensor common connection is connected to terminal B of each sensor. The signal voltage from terminal C of each sensor is sent to the appropriate terminal at the J2/P2 ECM connector.

108-3 Diagnostic Code and High Crankcase Pressure

Some atmospheric pressure sensors that are located in the engine block actually sense crankcase pressure rather than atmospheric pressure. With this type of installation, crankcase pressure of approximately 14 kPa (2 psi) can cause the 108-3 diagnostic code to be generated.

Before you proceed with this test, determine whether the sensor is sensing crankcase pressure or atmospheric pressure.

If the sensor is sensing crankcase pressure, connect Caterpillar Electronic Technician (ET) to the ECM and clear the diagnostic code. Do not start the engine. Maintain electrical power to the ECM. Wait at least 30 seconds for generation of the diagnostic code. Slowly wiggle the wiring for the sensor in an attempt to generate an intermittent code.

If the 108-3 code is generated, continue with the functional test.

If the 108-3 code is not generated, there is either a problem with high crankcase pressure or the code is intermittent, due to a loose connector or damaged wiring.

A plugged crankcase breather will cause excessive crankcase pressure. Leakage of the crankshaft seal can occur. Sealing of the piston rings can be lost. This will enable crankcase blowby to further increase the crankcase pressure.

If the piston rings do not seal, blowby will increase the crankcase pressure and the problem will become worse. Performance will deteriorate. The engine will have poor combustion. Deposits will build up on the pistons, on the valves, and in the cylinder heads. Downward pumping of the pistons against the increased crankcase pressure will further reduce the performance.

Sticking of the pistons will also increase the crankcase pressure. If the problem is not resolved, piston seizure will result. If a problem with a piston is suspected, do not operate the engine. Inspect the cylinder liner for scoring and for scuffing. Replace the piston rings and the cylinder liner, if necessary.

To eliminate crankcase pressure as the cause of the 108-3 diagnostic code, inspect the crankcase breather. If the breather is plugged, clean the breather or replace the breather. Make sure that the air passages for the breather's system are clear.

To verify that the plugged breather was the problem, operate the engine at a high load for at least 30 seconds. If the code does not recur, return the engine to service.

Illustration 1	g00692909
C-10 and C-12 Pressure sensors

Illustration 2	g00692936
3406E Pressure sensors

Illustration 3	g00693763
C-15, C-16 and C-18 Pressure sensors

Illustration 4	g00662235
Schematic for engine pressure sensors

Illustration 5	g00662237
Terminal locations for ECM

Illustration 6	g00810608
Sensor connector

Test Step 1. Check for Active +5 V Sensor Supply Diagnostic Codes

1. Connect the Caterpillar Electronic Technician (Cat ET) to the data link connector.

2. Turn the keyswitch 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:
   • 232-03 5 Volt Supply voltage high

   • 232-04 5 Volt Supply voltage low

Expected Result:

None of the preceding diagnostic codes are active.

Results:

• OK - Proceed to Test Step 2.

• Not OK -

  Repair: Perform the following diagnostic procedure: Troubleshooting, "5 Volt Engine Pressure Sensor Supply Circuit - Test".

  STOP

Test Step 2. Inspect Electrical Connectors And Wiring

1. Thoroughly inspect the J2/P2 ECM connector and the connectors for any suspect sensors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors that are associated with the active diagnostic code.

   Refer to Illustration 5.

3. Check the ECM connector (Allen Head Screw) for the proper torque of 6.0 N·m (55 lb in).

4. Check the harness and wiring for abrasion and pinch points from the sensors back 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.Clear all logged diagnostic codes.

  STOP

Test Step 3. Determine the Condition that is Present

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

2. Monitor the active diagnostic code screen on Cat ET.

3. Determine if the problem is related to a "voltage high" diagnostic code (open circuit) or a "voltage low" diagnostic code (short circuit).

Expected Result:

Either a "voltage low" diagnostic code (short circuit) is active or a "voltage high" diagnostic code (open circuit) is active.

Results:

• Voltage Low (Short) - A "voltage low" diagnostic code (short circuit) is active at this time. Proceed to Test Step 4.

• Voltage High (Open) - A "voltage high" diagnostic code (open circuit) is active at this time. Proceed to Test Step 7.

Test Step 4. Disconnect the Suspect Sensor

1. Turn the keyswitch to the OFF position.

2. Disconnect the sensor with the "voltage low" diagnostic code (short circuit).

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

4. Check for an active "voltage high" diagnostic code (open circuit) for the disconnected sensor.

Expected Result:

A "voltage high" diagnostic code (open circuit) for the disconnected sensor is now active.

Results:

• OK - A "voltage low" diagnostic code (short circuit) was active before disconnecting the sensor. A "voltage high" diagnostic code (open circuit) became active after disconnecting the sensor.

  Repair: Temporarily connect a new sensor.Check for active diagnostic codes.If the new sensor fixes the problem, reconnect the suspect sensor.If the problem returns, permanently install the new sensor.Verify that the repair eliminates the problem.

  STOP

• Not OK - There is a short circuit between the sensor and the ECM.

  Repair: Leave the suspect sensor disconnected.

  Proceed to Test Step 5.

Test Step 5. Create an Open Circuit at the ECM

1. Turn the keyswitch to the OFF position.

2. Remove the signal wire of the suspect sensor from the P2 ECM connector.

3. Turn the keyswitch to the ON position.

4. Check for active diagnostic codes.

Expected Result:

A "voltage high" diagnostic code (open circuit) became active after disconnecting the signal wire.

Results:

• OK - A "voltage low" diagnostic code (short circuit) was active before disconnecting the sensor. A "voltage high" diagnostic code (open circuit) became active after disconnecting the sensor. Proceed to Test Step 6.

• Not OK - There is still a "voltage low" diagnostic code (short circuit).

  Repair: Connect a test ECM.If the test ECM fixes the problem, reconnect the suspect ECM.If the problem returns, permanently replace the suspect ECM.Verify that the repair eliminates the problem.

  STOP

Test Step 6. Check the Resistance of the Harness

1. Turn the keyswitch to the OFF position.

2. Verify that the suspect sensor is disconnected.

3. Measure the resistance between terminal B (Pressure Sensor Common) and terminal C (Signal) of the connector for the suspect sensor on the engine harness.

Expected Result:

The resistance is greater than 20,000 Ohms, or "OL" is displayed on the multimeter.

Results:

• OK - The resistance is greater than 20,000 Ohms, or "OL" is displayed on the multimeter.

  Repair: Check the signal wire for a short to ground.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  STOP

• Not OK - There is a short between the pressure sensor common and the signal wire.

  Repair: Locate the short between the pressure sensor common and the signal wire.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  STOP

Test Step 7. Measure the Sensor Supply Voltage

1. Turn the keyswitch to the OFF position.

2. Disconnect the suspect sensor.

3. Turn the keyswitch to the ON position.

4. Measure the voltage from terminal A (Pressure Sensor +5V) to terminal B (Pressure Sensor Common).

Expected Result:

The voltage is 5.0 ± 0.16 VDC.

Results:

• OK - The sensor supply voltage is correct.

  Repair: Leave the sensor disconnected.

  Proceed to Test Step 8.

• Not OK - The sensor supply voltage is out of the range.

  Repair: Check the 5 volt supply wire for an open circuit.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  STOP

Test Step 8. Create a Short Circuit at the Sensor

1. Turn the keyswitch to the ON position.

2. Monitor the active diagnostic code screen.

3. Install a jumper wire between terminal C (Signal) and terminal B (Pressure Sensor Common) of the sensor connector. Wait at least 15 seconds for activation of the "voltage low" diagnostic code (short circuit).

Expected Result:

A "voltage low" diagnostic code (short circuit) is active when the jumper wire is installed. A "voltage high" diagnostic code (open circuit) is active when the jumper wire is removed.

Results:

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

  Repair: Temporarily connect a new sensor.If the new sensor fixes the problem, reconnect the suspect sensor.If the problem returns, permanently replace the suspect sensor.Verify that the repair eliminates the problem.

  STOP

• Not OK - The "voltage high" diagnostic code (open circuit) remains active when the jumper wire is installed.

  Repair: Remove the jumper wire.

  Proceed to Test Step 9.

Test Step 9. Create a Short Circuit at the ECM

1. Turn the keyswitch to the OFF position.

2. Disconnect the J2/P2 ECM connector.

3. Turn the keyswitch to the ON position.

   A "voltage high" diagnostic code (open circuit) should be active for the suspect sensor.

4. Monitor the active diagnostic code screen. Wait at least 15 seconds for activation of the code.

   Note: When the P2 ECM connector is disconnected, all of the "voltage high" diagnostic codes (open circuit) for the pressure sensors will be active. This is normal.

5. Install a jumper wire between the terminal for the signal of the suspect sensor and the pressure sensor common on the ECM. Wait at least 15 seconds for activation of the "voltage low" diagnostic code (short circuit).

Expected Result:

A "voltage low" diagnostic code (short circuit) is active for the suspect sensor.

Results:

• OK - The ECM is operating properly.

  Repair: Leave the P2 ECM connector disconnected.

  Proceed to Test Step 10.

• Not OK - The "voltage high" diagnostic code (open circuit) is still active when the jumper wire is installed.

  Repair: Temporarily connect a test ECM.If the test ECM fixes the problem, reconnect the suspect ECM.If the problem returns, permanently replace the ECM.Verify that the repair eliminates the problem.

  STOP

Test Step 10. Check the Resistance of the Harness

1. Turn the keyswitch to the OFF position.

2. Verify that the suspect sensor is disconnected.

3. Check the resistance between terminal A (Pressure Sensor +5V) and terminal C (Signal) of the connector for the suspect sensor on the engine harness.

Expected Result:

The resistance is greater than 20,000 Ohms or "OL" is displayed on the multimeter.

Results:

• OK - There is an open circuit in the signal wire.

  Repair: Locate the open in the signal wire.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  STOP

• Not OK - There is a short between the 5 volt supply and the signal wire.

  Repair: Locate the short between the 5 volt supply and the signal wire.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  STOP