General Information - Miscellaneous Sensors
A number of sensors provide information to your vehicle's on-board computer or PCM (Powertrain Control Module). The PCM and sensors work together to monitor engine components to achieve optimum performance, efficiency and fuel economy. The PCM is also connected to a variety of "output actuators" - mechanical devices - which respond to the conditions that the sensors monitor. These include the fuel injectors, ignition coils, and various relays and solenoids.
Below are a number of examples of the different types of sensors inside your vehicle.
Note: this is a general description. Consult a repair manual written specifically for your car, truck, van or SUV for exact descriptions.
The Accelerator Pedal Position (APP) sensor is part of the accelerator control system for vehicles that do not have a conventional accelerator cable. Its job is to constantly monitor the angle of the accelerator pedal. It then sends this data to the PCM. The PCM controls an output actuator that is connected to the throttle. This output actuator opens and closes the throttle to the proper position dictated by the APP sensor so that the engine receives the proper amount of air and fuel.
The Camshaft Position sensor (CMP) produces a signal that the PCM uses to monitor the position of the camshaft. This information allows the CMP sensor to identify the #1 cylinder so that, in turn, the PCM can time the firing order of the spark plugs and the firing sequence of the fuel injectors.
The Crankshaft Position sensor (CKP) produces a signal that the PCM uses to monitor the position of the crankshaft. The PCM uses this data to synchronize ignition timing with fuel injector timing. Synchronizing in this manner controls spark knock and allows the PCM to detect misfires.
The Engine Coolant Temperature (ECT) sensor sends a signal to the PCM. The PCM can then determine the temperature of the coolant. The ECT sensor tells the PCM when the engine is warmed up enough to then direct the coolant to the radiator. The data from the ECT also helps the PCM control the fuel/air mixture ratio and ignition timing, and helps the PCM to determine when to turn the Exhaust Gas Recirculation system off or on.
A fuel tank pressure sensor measures fuel tank pressure when the PCM tests the Evaporative Emissions Control (EVAP) system. It also helps control fuel tank pressure. It does this by signaling the EVAP system to purge the tank if pressure is excessive.
An Inlet Air Temperature (IAT) sensor monitors the temperature of the air going into the engine and then sends a signal to the PCM.
A knock sensor interestingly is made of a special kind of crystal called a "piezoelectric" crystal. This crystal material produces an electrical charge when bumped or jarred. When your engine is "knocking," (in other words when gases that remain in your vehicle's cylinder[s] after the spark plug fires spontaneously ignite and cause a "pinging" or "knocking" sound), the piezoelectric knock sensor is jarred and produces an electrical signal. The PCM records this signal and retards the ignition accordingly. Caution: If your engine's emits a pinging or knocking sound and you do not take care of it, serious engine problems could occur.