SEAL 2725642 - Caterpillar

System Operation Description:Use this procedure to troubleshoot any suspect problems with the following sensors:
Primary engine speed/timing sensor
Secondary engine speed/timing sensorThis 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 signal
342-11 Secondary Engine Speed Sensor mechanical failureThe engine uses two engine speed/timing sensors. The secondary engine speed/timing sensor picks up the camshaft gear and the primary engine speed/timing sensor picks up the crankshaft gear. Both of the engine speed/timing sensors detect the reference for engine speed and timing from a unique pattern on the respective 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.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 engine speed/timing 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 on 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.
Illustration 1 g01146558
C-10