3126B Marine Engines Caterpillar

Use this procedure to troubleshoot the system only under the following conditions:

• There is an active diagnostic code or an easily repeated diagnostic code that is associated with the engine speed/timing circuit.

• You have been directed here from another procedure.

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

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 the load. If the engine is running and the signal from one of the sensors is lost, no noticeable change in engine performance will be noticed.

The engine will start and the engine will run when only one sensor signal is present from either of the sensors. The loss of the signal from both of the sensors during engine operation will result in the termination of injection and the shutting down the engine by the ECM. The loss of the signal from both of the sensors during start-up will prevent the engine from starting.

Both sensors are magnetic sensors. The two sensors are not interchangeable. Do not switch the positions of the sensors. The two sensors must be replaced as a pair. If the sensors are replaced, a timing calibration is not necessary for the engine.

If a replacement of the ECM is required, the ECM parameters can be transferred from the suspect ECM to the replacement ECM. This feature is only possible if the existing ECM can communicate with the electronic service tool.

When the sensors are being installed, complete all of the following tasks:

• Lubricate the O-ring with oil.

• Ensure that the sensor has a connector face seal inside the connector body. If a seal is damaged or missing, replace the seal.

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

• Ensure that the connector is latched on both sides.

• Ensure that the harness is properly secured, and ensure that the harness is attached to the harness clip.

Illustration 1	g01051526
Schematic

Test Step 1. Check for Diagnostic Codes

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

2. Turn the key switch to the ON position.

3. Check for one of the following diagnostic codes:
   • 320-02

   • 320-11

   • 342-02

   • 342-11

   Note: If the diagnostic code is logged but not active, run the engine until the engine is at normal operating temperature. The problem may only occur when the engine is at the normal operating temperature.

   Note: If the engine will not start, monitor the engine rpm on the electronic service tool while the engine is being cranked. The electronic service tool may need to be powered from another battery while the engine is being cranked. This is done so the electronic service tool will not reset.

Expected Result:

One or more of the diagnostic codes that are listed above are logged or active.

Note: If the engine rpm was not indicated on the electronic service tool, select "No Engine rpm".

Results:

• OK - There is an active diagnostic code or a Logged diagnostic code. Proceed to Test Step 3.

• Not OK - None of the codes that are listed are active diagnostic codes or logged diagnostic codes and the engine is not running properly.

  Repair: Refer to the appropriate symptoms in the service manual.

  Stop.

• No Engine rpm - Engine rpm is not indicated on the electronic service tool. Proceed to Test Step 2.

Test Step 2. Check the Installation of the Sensors and the Bracket

Illustration 2	g00767308
Flange of the sensor and mounting bracket

1. Inspect the bracket in order to ensure that the installation allows the flange of the sensor to be flush against the front housing.

   Verify that the bracket is not bent.

   Note: The bracket cannot be replaced separately.

2. Ensure that the O-ring is installed on the sensor, and ensure that the O-ring is free of damage.

   Note: If the flange of the sensor is bent or if an obstruction is preventing the sensor from reading a good pattern, the engine will not start.

Expected Result:

The sensors and the bracket are properly installed.

Results:

• OK - The sensors and the bracket are properly installed. Proceed to Test Step 3.

• Not OK -

  Repair: Perform the following procedure in order to properly install the sensors and the bracket:

  1. Loosen the bolt that holds the sensor mounting bracket to the engine.

  2. Seat the sensor and tighten the bolt.

     If the sensor will not seat, repair the sensor or replace the sensor, as required.

     Note: The sensor must not be removed from the bracket.

  3. Ensure that the sensor is properly oriented and that the harness is secured in the proper location.

  4. Verify that the repair eliminates the problem.

  Stop.

Test Step 3. Measure the Sensor Resistance Through the Engine Harness

Illustration 3	g01065462

Illustration 4	g01056858
Terminal locations for ECM

1. Turn the key switch to the OFF position.

2. Thoroughly inspect ECM vehicle harness connector J2/P2. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Perform a 45 N (10 lb) pull test on the following wires in the ECM engine harness connector P2 that are associated with the engine speed/timing sensors:
   • P2:48 (primary speed/timing sensor positive)

   • P2:49 (primary speed/timing sensor negative)

   • P2:58 (secondary speed/timing sensor positive)

   • P2:59 (secondary speed/timing sensor negative)

   Refer to Illustration 3.

4. Ensure that the latch tab on 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. Repair the harness or repair the connector if a problem is found.

7. Ensure that the wiring harness is correctly routed and secured at the proper locations.

8. Ensure that the harness wiring is not pulled too tightly. When the harness wiring is pulled too tightly, vibrations or movement can cause intermittent connections.

9. Inspect the harness wiring for nicks and for abrasions.

10. If the harness and the connector are OK, disconnect ECM connector J2/P2.

11. Use the following procedure to measure the sensor resistance (Ohms) for the primary speed/timing sensor:

    Refer to Illustration 3.

    1. Use a multimeter to measure the resistance from P2:48 (primary speed/timing sensor positive) to P2:49 (primary speed/timing sensor negative).

    2. Check for an intermittent open circuit or short circuit by moving the harness while the measurement for resistance is being taken. Pull the wires that are directly behind the sensors or shake the wires that are directly behind the sensors.

       Resistance ... 110 to 200 Ohms

12. Use the following procedure to measure the sensor resistance (Ohms) for the secondary speed/timing sensor:

    Refer to Illustration 3.

    1. Use a multimeter to measure the sensor resistance (Ohms) from P2:58 (secondary speed/timing positive) to P2:59 (secondary speed/timing negative).

    2. Check for an intermittent open circuit or short circuit by moving the harness while the measurement for resistance is being taken. Pull the wires that are directly behind the sensors or shake the wires that are directly behind the sensors.

       Resistance ... 1000 to 1200 Ohms

Expected Result:

The readings agree with the values that are listed above.

Results:

• OK - Neither a short circuit nor an open circuit is indicated. Proceed to Test Step 5.

• Not OK - The sensor resistance is not within the acceptable range when the sensor resistance is measured through the engine harness. Proceed to Test Step 4.

Test Step 4. Measure the Resistance of the Sensor at the Sensor

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

2. Disconnect the suspect sensor from the engine harness.

3. Thoroughly inspect ECM engine harness connectors for the sensors J401/P401 or J402/P402. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

4. Use the following procedure to measure the sensor resistance (Ohms) for the primary sensor at the connector between terminal 1 and terminal 2:

   1. Use a multimeter to measure the sensor resistance (Ohms) from J401:2 to J401:1.

      Terminal 2 of the sensor connector is primary speed/timing positive.

      Terminal 1 of the sensor connector is primary speed/timing negative.

      Resistance ... 110 to 200 Ohms

5. Use the following procedure to measure the sensor resistance (Ohms) for the secondary camshaft position sensor at the sensor connector between terminal 1 and terminal 2:

   1. Use a multimeter to measure the sensor resistance (Ohms) from J402:2 to J402:1.

      Terminal 2 of the sensor connector is secondary speed/timing positive.

      Terminal 1 of the sensor connector is secondary speed/timing negative.

      Resistance ... 1000 to 1200 Ohms

Note: Timing calibration is not necessary following replacement of the speed/timing sensors. Refer to the information in the System Operation Section regarding the installation of sensors.

Expected Result:

The readings agree with the values that are listed above.

Results:

• OK - The sensor resistance is correct. However, it is still possible that there is a problem with the sensor. Proceed to Test Step 5.

• Not OK - The sensor resistance is out of the specified range.

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

  1. Before installing the new sensor, measure the resistance of the new sensor.

     Note: If the new sensor resistance is not in the correct range, inspect the wiring harness for damage.

     If the new sensor resistance is in the correct range, install the new sensor in the engine, as follows:

     1. Loosen the bolt that holds the sensor mounting bracket to the engine.

     2. Ensure that one O-ring is installed and free of damage.

     3. Seat the sensor and tighten the bolt.

        Note: The sensor must not be removed from the bracket.

     4. Ensure that the sensor is properly oriented and that the harness is secured in the proper location.

  2. Verify that the repair eliminates the problem.

  Stop.

Test Step 5. Check for a Short Circuit in the Wiring Harness

1. Disconnect the J2/P2 ECM connector.

2. Measure the following resistances at the P2 connector:

   Primary "top" speed/timing circuit

   • Measure the resistance between P2-48 and each individual socket on the J2 connector. Then measure the resistance between P2-48 and the ECM ground connection.

   • Measure the resistance between P2-49 and each individual socket on the J2 connector. Then measure the resistance between P2-49 and the ECM ground connection.

   Secondary "bottom" speed/timing circuit

   • Measure the resistance between P2-58 and each individual socket on the J1 connector. Then measure the resistance between P2-58 and the ECM ground connection.

   • Measure the resistance between P2-59 and each individual socket on the J1 connector. Then measure the resistance between P2-59 and the ECM ground connection.

Expected Result:

The resistance is greater than 20,000 Ohms for each measurement.

Results:

• OK - The circuit for the suspect sensor is not shorted in the harness. Proceed to Test Step 6.

• Not OK - There is a short circuit in the harness.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  Stop.

Test Step 6. Check for an Open Circuit in the Harness

1. Fabricate a jumper wire with pins at both ends.

2. Install the jumper wire into the appropriate ECM connector and then measure the resistance of the circuit.

   Primary "top" speed/timing circuit

   • Install the jumper wire to short P2:49 (primary speed/timing -) and P2:48 (primary speed/timing +) together.

   • Measure the resistance between P401:1 (primary speed/timing -) and P401:2 (primary speed/timing +).

   Secondary "bottom" speed/timing circuit

   • Install the jumper wire to short P2:59 (secondary speed/timing -) and P2:58 (secondary speed/timing +) together.

   • Measure the resistance between P402:1 (secondary speed/timing -) and P402:2 (secondary speed/timing +).

3. Remove the jumper wire.

Expected Result:

The resistance is less than 10 Ohms when the jumper wire is installed.

Results:

• OK - The circuit for the suspect sensor is not open in the harness. The sensor appears to be OK. However, it is possible that there is still a problem with the sensor. Proceed to Test Step 7.

• Not OK - There is an open circuit or excessive resistance in the harness or connectors.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  Stop.

Test Step 7. Test the Operation

1. Reconnect the sensor to the harness and reconnect the harness to the ECM.

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

Expected Result:

The engine operates normally.

Results:

• OK - The engine operates normally. There are no active diagnostic codes for the speed/timing sensor. The initial diagnostic code was probably caused by a poor electrical connection in one of the harness connectors. Stop.

• Not OK - The engine did not operate normally. A diagnostic code was activated for the speed/timing sensor. There may be a problem with the speed/timing sensor or with the ECM. Proceed to Test Step 8.

Test Step 8. Switch the Sensor

1. Turn the keyswitch to the OFF/RESET position.

2. Remove the original speed/timing sensor. Install an engine speed/timing sensor that is known to be good.

3. Turn the keyswitch to the ON position.

Expected Result:

The problem seems to be resolved. There are no active diagnostic codes for the speed/timing sensor.

Results:

• OK - Switching the sensor resolved the problem. There are no active diagnostic codes. You may want to install a new sensor before resuming normal operation. Stop.

• Not OK - The problem was not resolved by switching the sensors. A diagnostic code was activated. The wiring and the sensor are apparently OK. There may be a problem with the ECM.

  Repair: Exit this procedure and perform this procedure again. If the condition is not resolved, install a new ECM according to Troubleshooting, "Replacing the ECM".Verify that the problem is resolved.

  Stop.