3126B and 3126E On-highway Engines Caterpillar

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 diagnostic codes for the following sensors:

• Boost pressure sensor

• Oil pressure sensor

• Barometric pressure sensor

• Injection actuation pressure sensor

Use this procedure for the following diagnostic codes:

• 100-3 Engine Oil Pressure voltage high

• 100-4 Engine Oil Pressure voltage low

• 102-3 Boost Pressure Sensor voltage high

• 102-4 Boost Pressure Sensor voltage low

• 102-7 Boost Pressure not responding

• 108-3 Barometric Pressure Sensor voltage high

• 108-4 Barometric Pressure Sensor voltage low

• 164-3 Injection Actuation Pressure voltage high

• 164-4 Injection Actuation Pressure voltage low

The troubleshooting procedures for the diagnostic codes of each pressure sensor are identical. The Engine Control Module (ECM) sends a +5 V supply to terminal A for 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 J2 ECM connector.

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 -3 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.

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 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 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	g01151304
Schematic for the engine pressure sensors

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.

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Illustration 2	g01151317
Left side engine view (typical example) (1) Injection actuation pressure sensor (2) Atmospheric pressure sensor (3) Boost pressure sensor (4) Engine oil pressure sensor (option) (5) J2/P2 ECM connector

2. Thoroughly inspect ECM connector (5) . Also inspect the connectors for pressure sensors (1) , (2) , (3) , and (4) . Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

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Illustration 3	g01152507
P1 ECM connector (P2-2) +5 V pressure sensor supply (P2-3) Sensor return (P2-14) Barometric pressure (P2-24) Engine oil pressure (P2-27) Injection actuation pressure (P2-40) Boost pressure (P2-41) +5 V oil pressure sensor supply (P2-42) Oil pressure sensor return

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Illustration 4	g01123211
Connectors for the sensors (A) Supply (B) Return (C) Signal

3. 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.

4. Check the torque of the allen head screw on the ECM connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

5. Check the harness and wiring for abrasions and for pinch points from the sensors back to the ECM.

Expected Result:

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

Results:

• OK - The harness and wiring are OK. Proceed to Test Step 2.

• Not OK -

  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 coupled.Verify that the problem is resolved.

  STOP

Test Step 2. Check the Voltage on the +5 V Supply Wire

1. Turn the keyswitch to the OFF position.

2. Disconnect the harness connectors for the following sensors:
   • 100-3 Engine Oil Pressure voltage high

   • 100-4 Engine Oil Pressure voltage low

   • 102-3 Boost Pressure Sensor voltage high

   • 102-4 Boost Pressure Sensor voltage low

   • 102-7 Boost Pressure not responding

   • 108-3 Barometric Pressure Sensor voltage high

   • 108-4 Barometric Pressure Sensor voltage low

   • 164-3 Injection Actuation Pressure voltage high

   • 164-4 Injection Actuation Pressure voltage low

3. Turn the keyswitch to the ON position.

4. Measure the voltage between terminals A (supply) and B (return) at each sensor connector on the engine harness.

5. Turn the keyswitch to the OFF position.

6. Connect all of the sensors.

Expected Result:

Each voltage measurement is 5.0 ± 0.2 VDC.

Results:

• OK - Each voltage measurement is 5.0 ± 0.2 VDC. Proceed to Test Step 3.

• Not OK - At least one voltage measurement is not 5.0 ± 0.2 VDC.

  Repair: Refer to Troubleshooting, "Engine Pressure Sensor Supply Circuit - Test".

  STOP

Test Step 3. Check for Active Diagnostic Codes

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

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

3. Use Cat ET to check for active diagnostic codes. Wait at least 15 seconds so that any codes may become active. Look for an active diagnostic code for an engine pressure sensor.

4. Determine if the problem is related to a -3 diagnostic code or to a -4 diagnostic code.

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active for the engine pressure sensors.

  Repair: If any of the above codes are logged and the engine is not running properly, refer to Troubleshooting, "Troubleshooting Without a Diagnostic Code".If the engine is running properly at this time, there may be an intermittent problem in a harness that is causing the codes to be logged. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Active -4 Code - A -4 diagnostic code is active. Proceed to Test Step 4.

• Active -3 code - A -3 diagnostic code is active. Proceed to Test Step 5.

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

1. Turn the keyswitch to the OFF position.

2. Disconnect the harness connector of the sensor with the -4 diagnostic code.

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

4. Use Cat ET to check for active diagnostic codes. Check for an active -3 diagnostic code for the disconnected sensor.

5. Turn the keyswitch to the OFF position.

Expected Result:

A -3 diagnostic code is now active for the disconnected sensor.

Results:

• OK - A -4 diagnostic code was active before you disconnected the sensor. A -3 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.

  STOP

• Not OK - A -4 diagnostic code was active before you disconnected the sensor. The -4 diagnostic code remained after the sensor was disconnected. Leave the sensor disconnected. Proceed to Test Step 8.

Test Step 5. Check the Pull-up Voltage at the Sensor Connector

1. Turn the keyswitch to the ON position.

2. Disconnect the suspect sensor.

3. Measure the voltage between terminals C (signal) and B (return) at the harness connector for the suspect sensor.

4. Turn the keyswitch to the OFF position.

Expected Result:

The voltage is 5 ± 2 VDC.

Results:

• OK - The voltage is 5.0 ± 2 VDC. The signal wire to the ECM from the sensor connector is OK.

  Repair: The open circuit is in the sensor or the wire between the sensor and the sensor connector. Temporarily connect a new sensor to the engine harness. Do not install the sensor in the engine. Verify that no diagnostic codes are active for the new sensor before you permanently install the sensor.

  STOP

• Not OK - The voltage is not 5.0 ± 2 VDC. Proceed to Test Step 6.

Test Step 6. Check the Signal Wire for a Short Circuit

1. Turn the keyswitch to the OFF position.

2. Disconnect the J1/P1 and J2/P2 connectors.

3. Disconnect the harness connector for the suspect sensor.

4. Identify the terminal for the signal wire on the ECM connector that is appropriate for the suspect sensor. Measure the resistance between the appropriate terminal and the remaining terminals on both ECM connectors.

5. Measure the resistance between the appropriate terminal and the engine ground.

6. Connect the J1/P1 and J2/P2 connectors. Connect the connectors for the suspect sensor.

Expected Result:

Each resistance measurement indicates an open circuit.

Results:

• OK - Each resistance measurement indicates an open circuit. Proceed to Test Step 7.

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

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

  STOP

Test Step 7. Create a Short at the Harness Connector

1. Turn the keyswitch to the OFF position.

2. Install a jumper wire with Deutsch sockets on each end between terminals B (return) and C (signal) on the harness connector for the suspect sensor.

3. Turn the keyswitch to the ON position.

Note: Monitor Cat ET for diagnostic codes before installing the jumper wire and after installing the jumper wire.

4. Use Cat ET to check for active diagnostic codes. Wait at least 15 seconds so that any codes may become active. Look for a -4 diagnostic code.

5. Remove the jumper wire.

6. Turn the keyswitch to the OFF position.

Expected Result:

A -4 diagnostic code was active when the jumper wire was installed. A -3 diagnostic code became active when the jumper wire was removed.

Results:

• OK - A -4 diagnostic code was active when the jumper wire was installed. A -3 diagnostic code became active when the jumper wire was removed. 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 new sensor, permanently install the new sensor. Clear any logged diagnostic codes.Verify that the problem is resolved.

  STOP

• Not OK - A -4 diagnostic code was active when the jumper wire was installed. The -4 code remained when the jumper wire was removed. Proceed to Test Step 8.

Test Step 8. 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. Disconnect the J2/P2 connectors.

   2. Remove the signal wire for the suspect sensor from the ECM connector.

   3. Remove the sensor return from the ECM connector.

      Note: Disconnecting the return wire from the ECM will generate a -3 diagnostic code for all of the sensors. Ignore the additional codes. Troubleshoot the original diagnostic code and clear the codes when you are finished.

   4. Connect the J2/P2 connectors.

3. Turn the keyswitch to the ON position.

4. Monitor Cat ET for active diagnostic codes. Wait at least 15 seconds so that any codes may become active.

   A -3 diagnostic code should be active for the suspect sensor.

5. Turn the keyswitch to the OFF position.

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

   1. Disconnect the J2/P2 connectors.

   2. Install a jumper wire between the terminal for the sensor signal wire and the return wire at the P2 ECM connector.

   3. Connect the J2/P2 connectors.

7. Turn the keyswitch to the ON position.

8. Monitor Cat ET for active diagnostic codes. Wait at least 15 seconds so that any codes may become active.

   A -4 diagnostic code should be active when the wire jumper is installed.

9. Turn the keyswitch to the OFF position.

10. Remove the jumper wire. Return the wiring to the original configuration.

Expected Result:

A -3 diagnostic code was active when the signal wire was removed from the ECM connector. A -4 diagnostic code became active when the signal wire was connected to the return wire.

Results:

• OK - The ECM is operating properly. There is a problem 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. The problem may be in a connector. Repair the return wire and/or the connector. Replace parts, if necessary.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 and/or the connector. Replace parts, if necessary.Verify that the problem is resolved.

  STOP

• Not OK - One of the following conditions exists: The -3 diagnostic code is not active when the signal wire is disconnected. The -4 diagnostic code 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