GEARBOX GP 3648420 - Caterpillar

Illustration 1 g00104842
(1) Primary speed/timing sensor. (2) Backup speed/timing sensor.
If primary speed/timing sensor (1) cannot sense engine speed, the "DIAGNOSTIC" lamp will indicate a diagnostic fault code which will be logged in the ECM memory. If primary speed/timing sensor (1) cannot sense engine speed, the automatic default will use backup speed/timing sensor (2). The backup speed/timing sensor will be used until the primary speed/timing sensor is replaced.Speed/Timing Sensor Failure
If any of the following conditions are present, a speed/timing sensor failure may have occurred:
The speed/timing sensor output has opened.
The speed/timing sensor is shorted to ground.
The speed/timing sensor is shorted to supply.
The speed/timing sensor is missing pulses.
The speed/timing sensor has extra pulses.Intermittent failure causes erratic engine control. The electronic control system will detect a primary speed/timing sensor failure. The operator will be warned through the diagnostic lamp.