Most car owners probably don’t know their vehicle is equipped with a crankshaft position sensor until the engine dies, won’t start, or begins to malfunction.
Then, when the car is in the auto repair shop, they discover they need a new one. If there was ever an inconvenient time for your vehicle to report that you need a repair or replacement, this would be it.
The crankshaft position sensor, usually mounted near or on the crankshaft, tells the engine computer how fast the engine is rotating. This is how the control unit knows when the spark plugs should ignite the air-fuel mixture and, in some engines, when to inject fuel. These sensors are used on virtually all engines equipped with a distributorless ignition system.
If the starter sensor fails, the computer won’t know how to set the ignition timing, so the engine may stop running or refuse to start. Engine misfiring is also a symptom, which may eventually trigger the check engine light. The engine may run roughly, or acceleration may also be affected. Excessive heat is a common reason for these sensors to fail, and they may also stop working due to faulty electrical connections or wiring.
Some vehicles also have a camshaft position sensor that allows the engine computer to monitor the position of the camshafts (or camshaft), which open and close the valves, for more precise fuel and ignition management.
These sensors are not listed as routine maintenance items, but they often fail without warning. For this reason, some repair shops recommend replacing them on high-mileage engines as a preventive measure. The cost can vary depending on the shop, the engine, and the age of the car in question.
Since a faulty sensor doesn’t always trigger the check engine light – and some of the same symptoms could be caused by other problems in the fuel or ignition systems – the sensors should be tested with a diagnostic scanner or a multimeter before deciding to replace them. This is something a mechanic at a reputable repair shop would do before performing the sensor repair or replacement work.