Subaru Sensors Explained

by 1 August 02, 2009

Cam/Crankshaft position sensors - provides information from which the ECU can determine the exact rotational position of the engine, RPM and rate of acceleration. This is used to enable sequential fuel injection, or the control of individual fuel injectors, in addition to sophisticated miss-fire detection functions. Base ignition timing is also calculated from these two sensors.Camshaft position - on engines equipped with AVCS, additional sensors in the cylinder head monitor camshaft timing for closed loop valve timing control.Air mass sensor - calculates the actual weight of incoming intake charge and is a major determining parameter used by the ECU to calculate both injection time and ignition advance. Flash 02 and later equipped air mass sensors feature an in-built air temperature sensor that further improves sensor accuracy.Intake air temperature - Subaru STi only, (MY99/00), measures inlet air temperature for fine tuning ignition and boost compensations. Manifold pressure or MAP sensor - monitors manifold air pressure. Used by the Subaru ECU to determine injection time, ignition advance, boost control as well as an overboost safety cut function.Throttle pedal position sensor - DBW equipped engines use this sensor to "request" a given throttle position depending how hard the driver stands on the "loud" pedal.Throttle position sensor (TPS) - DBW equipped engines have two sensors measuring actual throttle butterfly position at the engine. Used to verify that commanded throttle position is being applied correctly. Non-DBW equipped engines have only one TPS sensor. TPS is another determining factor in the calculation of fuel and ignition delivery.Front and rear Lambda or "Oxygen" sensors- used by the engine for closed-loop fuel control and the monitoring of catalytic converter efficiency. Cat converters operate efficiently only around a very narrow air fuel ratio band of around lambda 0.99 or 14.64:1 in air fuel ratio.Engine coolant temperature sensor - used to adjust fuel mixtures and engine idle speed for cold starts, and to switch radiator cooling fans on and off. Knock sensor - a specially tuned microphone that the Subaru ECU uses to "listen" for the tell-tale sounds of detonation. Ignition timing and fuel mixtures are modified from feedback supplied by this sensor.Vehicle speed sensor - cooling fan operation, idle speed, speed limiters (JDM models) and fuel shut-off on deceleration are modified in reference to road speed. Boost control is also modified to provide "soft" speed limiting by reducing boost pressure at high road speeds on certain models.


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