Redundant sensor apparatus for determining engine speed and timing values

An engine control system includes a speed sensor apparatus for providing signals to an engine control module (ECM) indicative of the speed and timing of an internal combustion engine. The apparatus includes a primary and a secondary Hall device affixed to one pole of a dipole magnet. Independent flexible circuits connect each of the Hall devices to an output connector adapted to receive a cable connected to the ECM. The magnet, primary and secondary sensors and primary and secondary flexible circuits are potted and encased within a sensor housing that is configured for sealed mounting to a housing surrounding the timing wheel of the engine. The outputs from the two sensors are independent of each other and are simultaneously provided to the ECM. The ECM includes means for providing the output from the primary sensor to engine control routines utilizing speed and timing information while the primary sensor is operational. Means are also provided that derive a phase difference value between the primary and secondary outputs. In the event that the primary sensor fails, the ECM modifies the secondary sensor output by the phase difference value and provides the modified output to the engine control routines. In this manner, the engine control routines are provided with a consistent and continuous speed and timing signal even when one sensor fails.