A manifold absolute pressure sensor (MAP) is one of the sensors used in an internal combustion engine's electronic control system. Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). This is necessary to calculate air density and determine the engine's air mass flow rate, which in turn is used to calculate the appropriate fuel flow. (See stoichiometry.)
An engine control system that uses manifold absolute pressure to calculate air mass uses the speed-density method. Engine speed (RPM) and air temperature are also necessary to complete the speed-density calculation. Not all fuel-injected engines use a MAP sensor to infer mass air flow; some use a MAF (mass air flow) sensor. Several makes use the MAP sensor in OBD II applications to test the EGR valve for functionality. Most notably General Motors uses this approach.
A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the throttle valve butterfly.
The sensor is usually a potentiometer, and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position).
The sensor signal is used by the engine control unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).
More advanced forms of the sensor are also used, for example an extra closed throttle position sensor (CTPS) may be employed to indicate that the throttle is completely closed.
Some ECUs also control the throttle position and if that is done the position sensor is utilised in a feedback loop to enable that control.
Related to the TPS are accelerator pedal sensors, which often include a wide open throttle (WOT) sensor. The accelerator pedal sensors are used in "drive by wire" systems, and the most common use of a wide open throttle sensor is for the kickdown function on automatic transmissions.
Modern day sensors are Non Contact type, wherein a Magnet and a Hall Sensor is used. In the potentiometric type sensors, two metal parts are in contact with each other, while the butterfly valve is turned from zero to WOT, there is a change in the resistance and this change is resistance is given as the input to the ECU.
Non Contact type TPS work on the principle of Hall Effect, wherein the magnet is the dynamic part which mounted on the butterfly valve spindle and the hall sensor is mounted with the body and is stationary. When the magnet mounted on the spindle which is rotated from zero to WOT, there is a change in the magnetic field for the hall sensor. The change in the magnetic field is sensed by the hall sensor and the hall voltage generated is given as the input to the ECU. Normally a two pole magnet is used for TPS and he magnet may be of Diametrical type or Ring type or segment type, however the magnet is defined to have a certain magnetic field.