The Crankshaft position sensor also known as the crank position sensor is an electronic device used in an engine to record the rate at which the crankshaft is spinning. This information is used by the ECU to control ignition and fuel injection. The sensor system consists of a rotating part, typically a disc, as well as a static part, the actual sensor. Typically a Hall Effect sensor is used as the static part requiring a magnet to be mounted somewhere in the periphery of the rotating disc, but other detection principles can also be employed i.e. optical or inductive.
The functional objective for the crankshaft position sensor is the task of sensing engine RPM in order to determine the position and rotational speed of the crank. Engine management systems use the information transmitted by the sensor to control things such as ignition timing and other important functions. The sensor can also relate other crucial data including the relation of the valves to the pistons. While there are several competing objectives in the fuel injection system it was primarily designed for controlling and improving:
- power output
- fuel efficiency
- emissions performance
- ability to accommodate alternative fuels
- driveability and smooth operation
- initial cost
- maintenance cost
- diagnostic capability
- range of environmental operation
The rotating disc of the sensor system does not necessarily have to be mounted directly on the crankshaft but can also be driven by a chain or toothed belt off the crankshaft as is the case in some Hondas where the crank position sensor is located in the distributor, effectively driven by the timing belt. Other locations include: The front of the crank on the engine block below or next to the water pump, on the main crank pulley or near the flywheel.
Sometimes the sensor may become burnt or worn out. The most likely causes of crankshaft position sensor failure are exposure to extreme heat when you have a gasket or crank problem, corruption from oil or other engine fluids that leaked onto the sensor, or wear over a long period of time. When it goes bad, it stops transmitting the signal which contains the vital data for the ignition and other parts in the system.
Signs of a problem
A bad crank position sensor can worsen the way the engine idles, the pistons fire, or the acceleration behaviour. If the engine is revved up with a bad or faulty sensor, it may cause misfiring, motor vibration or backfires. Accelerating might be hesitant, and abnormal shaking during engine idle might occur. In the worst case the car may not start.
The crankshaft sensor will have to be replaced if it is malfunctioning. Consult a local auto mechanic that specializes in the particular manufacturer of vehicle being driven to secure the parts and labor in order to get the vehicle running properly. Avoid employing used parts for integral engine components as they have a greater chance of failure than newer equipment.