DIAPHRAGM 9L7873 - Caterpillar

System Operation Description:The engine is designed to use two speed/timing sensors, the primary speed/timing sensor and the secondary speed/timing sensor. The engine speed/timing sensors provide information to the Electronic Control Module (ECM) by generating pulse signals as the timing reference ring rotates past the magnetic pickups on the sensors. Both sensors are magnetic sensors with an integral connector. The sensors must be serviced as a pair. If one sensor requires replacement, both sensors be replaced.The secondary engine speed/timing sensor provides continuous operation of the engine if the primary engine speed/timing sensor fails. The loss of signals from both engine speed/timing sensors will prevent the ECM from actuating the injectors. To prevent any unnecessary down time, correct any problems with the speed/timing circuit at the earliest possible convenience.The engine speed/timing sensors are magnetic sensors that provide a frequency that is directly proportional to engine speed. A unique tooth on the timing reference ring passes by