3126B Petroleum Engine Caterpillar

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

• Primary engine speed/timing sensor

• Secondary engine speed/timing sensor

This procedure covers the following diagnostic codes:

• 320-02 Speed/Timing Sensor Loss of Signal

• 320-11 Speed/Timing Sensor mechanical failure

• 342-02 Loss of Secondary Engine Speed signal abnormal

• 342-11 Secondary Engine Speed Sensor mechanical failure

The engine uses two engine speed/timing sensors. Both sensors detect the reference for engine speed and timing from a unique pattern on the camshaft gear. The Electronic Control Module (ECM) uses the pattern of the pulses in order to determine the position of the crankshaft. The ECM measures the time between the pulses that are created by the sensors as the gears rotate in order to determine rpm.

Under normal operation, the secondary engine speed/timing sensor is used to determine timing for starting purposes. The secondary engine speed/timing sensor is used to determine when the piston in the No. 1 cylinder is at the top of the compression stroke. When the timing has been established, the primary engine speed/timing sensor is then used to determine engine speed.

When the timing has been established, the ECM triggers each injector in the correct firing order at the correct time. The actual timing and duration of each injection is based on engine rpm and on load.

If the engine is running and the signal from one sensor is lost, no noticeable change in engine performance will be noticed. If the engine is running and the signals from both sensors are lost, fuel injection will be terminated and the engine will be shut down by the ECM.

The engine will start when only one sensor signal is present. The engine will not start if the signals from both sensors are lost.

Both sensors are magnetic sensors. The two sensors are not interchangeable. Do not switch the positions of the sensors. Replace the sensors as a set. If the sensors are replaced, a timing calibration is not necessary.

If a replacement of the ECM is required, the ECM parameters and the timing calibration can be transferred from the suspect ECM to the replacement ECM. Timing calibration will not be necessary. This feature requires the Caterpillar Electronic Technician (ET) and this feature is only possible if the existing ECM can communicate with Cat ET. Use the "Copy Configuration - ECM Replacement" feature on Cat ET.

Complete all of the following tasks when you install the speed/timing sensors:

• Ensure that an O-ring is installed on each sensor. If an O-ring is damaged or missing, replace the O-ring.

• Lubricate the O-rings with oil.

• Ensure that the sensor assembly is fully seated into the engine before tightening the bracket bolt.

• Ensure that each electrical connector is latched on both sides.

• Ensure that the harness is properly secured, and ensure that each tie-wrap is placed in the correct location.

Illustration 1	g01129282

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The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere.

Test Step 1. Check for Diagnostic Codes

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

2. Start the engine and run the engine until the engine is at normal operating temperature.

   Note: If the engine will not start, monitor the engine rpm on Cat ET while the engine is being cranked. Cat ET may need to be powered from another battery while the engine is being cranked.

3. Look for these codes on Cat ET:
   • 320-02

   • 320-11

   • 342-02

   • 342-11

Expected Result:

None of the codes are logged or active.

Note: If the engine will not start and Cat ET displayed 0 rpm during cranking, select "No Engine rpm".

Results:

• Ok - Neither code is active or logged.

  Repair: Refer to the appropriate symptoms in Troubleshooting, "Troubleshooting Without a Diagnostic Code".

  STOP

• Not OK - 320-02, 320-11, 342-02, or 342-11 is active or logged. Proceed to Test Step 4.

• No Engine rpm - Zero rpm is indicated on Cat ET while the engine is cranked. Proceed to Test Step 2.

Test Step 2. Check the Installation of the Sensor Assembly

1. Turn the keyswitch to the OFF position.

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Illustration 2	g01129316
Left side view (1) Mounting surface for the sensors (2) Flanges (3) Bracket

2. Inspect the bracket in order to ensure that the installation allows the flange of the sensor to be flush against the mounting surface.

   Verify that the bracket is not bent. If the bracket is bent or if an obstruction is preventing the sensor assembly from being installed correctly, the engine will not start.

   Note: The bracket cannot be replaced separately.

3. Remove the sensor assembly from the engine.

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Illustration 3	g01120279
Sensor assembly (4) O-ring

4. Ensure that one O-ring (4) is installed on each sensor. Check the O-rings for damage. Replace the O-rings, if necessary.

Expected Result:

The O-rings are installed on the sensors and the sensors are not damaged.

Results:

• OK - The sensor assembly's components are OK.

  Repair: Perform the following procedure in order to properly install the sensor assembly:

  1. Lubricate each O-ring with clean engine oil.

  2. Fully seat the sensor assembly in the engine.

     Note: If the sensor assembly will not fully seat into the engine, replace the sensor assembly.

  3. Tighten the bracket bolt.

  4. Connect the sensor's electrical connectors. Verify that the connectors are latched on both sides.

  5. Ensure that the harness is properly secured, and that the tie-wraps are placed in the correct location.

  Proceed to Test Step 4.

• Not OK - At least one of the sensor assembly's components is not OK.

  Repair: Obtain a new sensor assembly. Perform the following procedure in order to properly install the sensor assembly:

  1. Lubricate each O-ring with engine oil.

  2. Fully seat the sensor assembly in the engine.

     Note: If the sensor assembly will not fully seat into the engine, replace the sensor assembly.

  3. Tighten the bracket bolt.

  4. Connect the sensor's electrical connectors. Verify that the connectors are latched on both sides.

  5. Ensure that the harness is properly secured, and that the tie-wraps are placed in the correct location.
  Verify that the problem is resolved.

  STOP

Test Step 3. Inspect the Electrical Connectors and the Wiring

1. Thoroughly inspect J2/P2 ECM connector, P400 TC probe connector, J401/P401 primary engine speed/timing sensor connector, and J402/P402 secondary engine speed/timing sensor connector. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 4	g01129387
P2 terminations for the engine speed/timing sensors (P2-22) TDC probe + (P2-23) TDC probe − (P2-48) Primary engine speed/timing + (P2-49) Primary engine speed/timing − (P2-58) Secondary engine speed/timing + (P2-59) Secondary engine speed/timing −

2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the engine speed/timing sensors.

3. Check the torque of the allen head screws for the ECM connectors. Refer to Troubleshooting, "Electronic Service Tools" for the correct torque values.

4. Check the harness and the wiring for abrasion and for pinch points from each sensor back to the ECM.

Expected Result:

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

Results:

• OK - The harness and connectors appear to be OK. Proceed to Test Step 4.

• Not OK - The connectors and/or wiring are 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 completely coupled. Verify that the repair eliminates the problem.

  STOP

Test Step 4. Measure the Sensor Resistance through the Engine Harness

1. Disconnect the J2/P2 ECM connector.

2. If you are troubleshooting a problem with the primary engine speed/timing sensor, perform the following procedure:

   1. Measure the sensor's resistance between P2-48 primary engine speed/timing + and P2-49 primary engine speed/timing -.

   2. Check for an intermittent open circuit or for a short circuit by moving the harness while you take the resistance measurement. Pull the wires that are directly behind the sensor or shake the wires that are directly behind the sensor.

      Resistance at 25 °C (77 °F) ... 110 to 220 Ohms

3. If you are troubleshooting a problem with the secondary engine speed/timing sensor, perform the following procedure:

   1. Measure the sensor's resistance between P2-58 Secondary engine speed/timing + and P2-59 Secondary engine speed/timing -.

   2. Check for an intermittent open circuit or for a short circuit by moving the harness while you take the resistance measurement. Pull the wires that are directly behind the sensor or shake the wires that are directly behind the sensor.

      Resistance at 25 °C (77 °F) ... 1000 to 1300 Ohms

Expected Result:

The resistance measurement is within the specifications.

Results:

• OK - The resistance measurement is within the specifications. Neither a short circuit nor an open circuit is indicated.

  Repair: Perform the following procedure:

  1. Temporarily install a test ECM. Refer to Troubleshooting, "Replacing the ECM".

  2. Start the engine. Run the engine until the engine is at normal operating temperature.

  3. If the problem is resolved with the test ECM, connect the original ECM and verify that the problem recurs.

  4. If the problem returns with the original ECM, replace the ECM. Verify that the problem is resolved.

  STOP

• Not OK - The readings are not within the specifications. The sensor resistance is not within the acceptable range when the sensor resistance is measured through the engine harness. Proceed to Test Step 5.

Test Step 5. Measure the Resistance of the Sensor

1. Turn the keyswitch to the OFF position.

2. Disconnect the harness connector for the suspect sensor.

3. Thoroughly inspect the sensor's connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect".

4. Measure the sensor's resistance between terminals A and B.

Expected Result:

For the primary engine speed/timing sensor, the resistance measurement at 25 °C (77 °F) is between 110 and 200 Ohms. For the secondary engine speed/timing sensor, the resistance measurement at 25 °C (77 °F) is between 1000 and 1200 Ohms.

Results:

• OK - The reading is within the specification. There is a problem with the wiring between the engine speed/timing sensor and the ECM. 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

• Not OK - The reading is not within the specification. There is an electrical problem with the engine speed/timing sensor.

  Repair: Perform the following procedure in order to check and install the new sensor assembly:

  1. Before you install the new sensor assembly, measure the resistance of the new sensors.

     If the resistance measurements of the new sensors are within the specifications, install the new sensor assembly in the engine according to the following procedure:

     1. Loosen the bolt and remove the bolt that holds the sensor assembly to the engine.

     2. Ensure that O-rings are installed on the new sensor assembly. Verify that the O-rings are free of damage.

     3. Seat the sensor assembly and tighten the bolt.

        If the sensor will not seat, replace the sensor.

     4. Ensure that the harness is secured in the proper location. Verify that the repair eliminates the problem.

  STOP