Crankshaft Position Sensor – Diagnosis and Fix One of the first things they teach in any diagnostician or engine mechanics course is about two main sensors: the crankshaft position sensor and the camshaft position sensor. The reason is, these two play a vital role in getting the engine to start in the first place, and to keep it idling and running at a constant, smooth pace. So these, especially the crankshaft sensor, are the first items on our checklist when the car doesn’t start or idles roughly. The crankshaft position sensor, or CPS for short, is one of the more ingenious inventions relating to internal combustion engines due to its fairly simple concept and design and yet terribly important role in the operation of the engine. Before these things came along, engines relied on what was called a distributor for synchronizing the timing of fuel injection in diesel and ignition spark in petrol engines. And to get that sync, the distributor had to be manually adjusted to timing marks fitted for that purpose. Put simply, the CPS makes this process automatic.