Techmail

Similar to the ABS wheel-speed sensor unpacked last month, the crankshaft-position sensor is an inductive pickup mounted in close proximity to the teeth on the engine’s flywheel (ring gear). to get the mounting gap correct, there’s a tiny sacrificial plastic ring at the bottom of the sensor allowing a technician to push it right against the flywheel when installing. the flywheel has a set number of teeth, with usually a gap where a tooth is missing. this is to provide the trigger signal to the ECU so it records the crankshaft rotational position (and so too the position of the pistons). For stroke information and which cylinder will fire next, the ECU needs to identify the position of the camshaft to learn the status of each cylinder. this is done with a camshaft-position sensor. the correlation of these two sensors happens instantly during the first cranking of an engine.