Use this procedure to troubleshoot the electrical system if a problem is suspected with the primary engine speed/timing sensor or with the secondary engine speed/timing sensor. Use this procedure to troubleshoot the electrical system if a diagnostic code in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
|---|---|---|
| Code and Description | Conditions which Generate this Code | System Response |
| 190-8 Engine Speed Sensor abnormal frequency, pulse width, or period | The signal from the primary engine speed/timing sensor is intermittent or the signal has been lost. | The code is logged. If a valid signal is not received from the primary engine speed/timing sensor, the Electronic Control Module (ECM) will default to the secondary engine speed/timing sensor. The engine will shut down only if the signals from the primary engine speed/timing sensor and the secondary engine speed/timing sensor are abnormal. |
| 342-8 Secondary Engine Speed Sensor abnormal frequency, pulse width, or period | The signal from the secondary engine speed/timing sensor is intermittent or the signal has been lost. | The code is logged. If a valid signal is not received from the secondary engine speed/timing sensor, the ECM will default to the primary engine speed/timing sensor. The engine will shut down only if the signals from the primary engine speed/timing sensor and the secondary engine speed/timing sensor are abnormal. |
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 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 and the signal from the secondary camshaft sensor is ignored.
After locating the No. 1 cylinder, the ECM triggers each injector in the correct firing order and at the correct unit injector timing. The actual timing and duration of each injection is based on engine rpm and load. If the engine is running and the signal from the primary engine speed/timing sensor is lost, a slight change in engine performance will be noticed when the ECM performs the changeover to the secondary engine speed/timing sensor. Loss of the signal from the secondary engine speed/timing sensor during engine operation will not result in any noticeable change in engine performance. However, if the signal from the secondary engine speed/timing sensor is not present during start-up the following conditions may exist:
- The engine may require a slightly longer period of time to start-up.
- The engine may run rough for a few seconds until the ECM determines the proper firing order by using the primary engine speed/timing sensor only.
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 of 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 with an integral connector. The two sensors are not interchangeable. Do not switch the positions of the sensor. If the sensors are replaced, a timing calibration is not necessary for the engine.
Note: When the sensors are being installed, complete all of the following tasks:
- Lubricate the O-ring with oil.
- Ensure that the sensor is fully seated into the engine before tightening the bracket bolt.
- Ensure that the connector is properly latched.
- Ensure that the harness is properly secured, and ensure that the tie-wraps are placed in the correct location.
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| Illustration 1 | g01199875 |
Schematic for the engine speed/timing sensors | |
Test Step 1. Check for Diagnostic Codes
- Connect Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".
- Restore electrical power to the ECM.
- Start the engine and run the engine. The problem may occur when the engine is at any operating temperature. However, the problem is more likely to occur when the engine is at the normal operating temperature.
- If the engine will not start, monitor the engine speed 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. This is done so that Cat ET will not reset.
Note: Upon initial cranking, the status for engine speed may indicate that the engine speed signal is abnormal. This message should be replaced with an engine speed once the ECM is able to calculate a speed from the signal.
- Wait at least 30 seconds for activation of the diagnostic codes. Look for these codes on Cat ET:
- 190-8
- 342-8
- 190-8
Expected Result:
One or both of the diagnostic codes that are listed above are logged or active.
Note: If the engine will not start and Cat ET displayed 0 rpm during cranking, select "No Engine rpm".
Results:
- No Engine rpm - Engine rpm is not indicated on Cat ET. Proceed to Test Step 2.
- Active Code or logged code - There is an active diagnostic code or a logged diagnostic code for an engine speed/timing sensor. Proceed to Test Step 3.
Test Step 2. Inspect the Sensor Assembly
- Remove electrical power from the engine ECM.
- Visually inspect the sensor assembly without removing the sensor assembly from the engine. Flanges (2) must be flush against the surface of the front timing gear housing (1) in order to ensure proper operation.
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| Illustration 2 | g01180490 |
Typical left side engine view (1) Rear surface of the front timing gear housing (2) Mounting flange (3) Bracket | |
- Inspect bracket (3). Verify that the bracket securely holds the flanges of the sensors flush against the engine.
- 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.
- Remove the sensor assembly from the engine. Inspect each sensor. Ensure that the sensor is not damaged. Replace the sensor, if necessary.
- Ensure that one O-ring (4) is installed on each sensor. Check the O-rings for damage. Replace the O-rings, if necessary.
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| Illustration 3 | g01180501 |
Exploded view of the engine speed/timing sensors (4) O-ring seals | |
Expected Result:
Two undamaged O-ring seals are properly installed. The brackets are not bent. The flange for each sensor can be flush against the housing.
Results:
- OK - Two undamaged O-ring seals are properly installed. The brackets are not bent. The flange for each sensor can be flush against the housing.
Repair: Perform the following procedure in order to properly install a sensor assembly:
- Lubricate the O-ring seal with oil.
- Fully seat the sensor into the housing.
- Tighten the bracket bolt.
- Connect the connector and verify that the latch tab of 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.
Proceed to Test Step 3.
- Not OK - The sensor assembly has a mechanical problem.
Repair: Replace the sensor assembly.
- Lubricate the O-ring with oil.
Note: Do not switch the positions of the sensors. The sensors are not interchangeable. A timing calibration is not required when the sensors are replaced.
- Fully seat the sensor into the housing.
- Tighten the bracket bolt.
- Connect the connector and verify that the latch tab of 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.
STOP
Test Step 3. Inspect the Electrical Connectors and the Wiring
- Remove electrical power from the ECM.
- Thoroughly inspect the connectors for the engine speed/timing sensors (5) and (6). Refer to Troubleshooting, "Electrical Connectors - Inspect".
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| Illustration 4 | g01181799 |
Typical left side engine view (5) connector for the primary engine speed/timing sensor (6) connector for the secondary engine speed/timing sensor (7) J2/P2 ECM connector | |
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the engine speed/timing sensor.
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| Illustration 5 | g01339504 |
P2 connector (P2-25) Primary engine speed/timing signal (−) (P2-26) Timing calibration probe (+) (P2-35) Primary engine speed/timing signal (+) (P2-36) Timing calibration probe (−) (P2-46) Secondary engine speed/timing signal (+) (P2-47) Secondary engine speed/timing signal (−) | |
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| Illustration 6 | g01218763 |
Terminal locations at the connector for the speed/timing sensors (1) Engine speed/timing signal (−) (2) Engine speed/timing signal (+) | |
- Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Check the harness and wiring for abrasion and for pinch points from the engine speed/timing sensors to the ECM.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted. 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 4.
- Not OK - There is a problem in the connectors and/or wiring.
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 4. Measure the Sensor Resistance through the Engine Harness
- Remove electrical power from the ECM.
- Disconnect the J2/P2 ECM connector.
- If you are troubleshooting a problem with the primary engine speed/timing sensor, perform the following procedure:
- Measure the resistance from P2-35 (Primary engine speed/timing +) to P2-25 (Primary engine speed/timing −).
- 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 ... 75 to 230 Ohms
- If you are troubleshooting a problem with the secondary engine speed/timing sensor, perform the following procedure:
- Measure the resistance from P2-46 (secondary engine speed/timing +) to P2-47 (secondary engine speed/timing −).
- 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 ... 600 to 1800 Ohms
Expected Result:
The resistance measurements are within the specifications.
Results:
- OK - The resistance measurements are within the specifications. The wiring appears to be OK.
Repair: The sensors and the harness are OK.
- Temporarily connect a test ECM.
- If the problem is resolved with the test ECM, reconnect the suspect ECM.
- If the problem returns with the suspect ECM, replace the ECM.
STOP
- Not OK - At least one of the resistance measurements is not within the specifications. Proceed to Test Step 5.
Test Step 5. Measure the Resistance of the Sensor
- Disconnect the engine harness from the suspect sensor.
- For the primary engine speed/timing sensor, measure the resistance between terminal 2 (Primary engine speed/timing +) to terminal 1 (Primary engine speed/timing −).
Resistance ... 75 to 230 Ohms
- For the secondary engine speed/timing sensor, measure the resistance between terminal 2 (secondary engine speed/timing +) to terminal 1 (secondary engine speed/timing −).
Resistance ... 600 to 1800 Ohms
Expected Result:
The resistance measurement for the suspect sensor is within the specification.
Results:
- OK - The resistance measurement for the suspect sensor is within the specification. There is a problem with the wiring or there may be a problem with a connector.
Repair: Repair the connection and/or the wiring, when possible. Replace parts, if necessary. Twisted pair wiring is required. The wiring must have at least one twist per inch. Verify that the problem is resolved.
STOP
- Not OK - The resistance measurement for the suspect sensor is not within the specification. There is a problem with the sensor.
Repair: Replace the sensor assembly.Do not switch the positions of the sensors. The sensors are not interchangeable. A timing calibration is not required when the sensors are replaced. Perform the following procedure in order to replace the sensor assembly:
- Lubricate the O-ring seal with oil.
- Fully seat the sensor into the housing.
- Tighten the bracket bolt.
- Connect the connector and verify that the latch tab of 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.
STOP