Circuit Description

The supercharger inlet absolute pressure (SCIAP) sensor measures the pressure after the throttle body, but before the supercharger. Pressure in the intake manifold is affected by engine speed, throttle opening, air temperature, and barometric pressure (BARO). A diaphragm within the SCIAP sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates this action into electrical resistance. The SCIAP sensor wiring includes 3 circuits. The engine control module (ECM) supplies a regulated 5 volts to the sensor on a 5-volt reference circuit. The ECM supplies a ground on a low reference circuit. The SCIAP sensor provides a signal voltage to the ECM, relative to the pressure changes, on the SCIAP sensor signal circuit. The ECM converts the signal voltage input to a pressure value.

Under normal operation the highest pressure that can exist in the intake manifold is equal to BARO. This occurs when the vehicle is operated at wide-open throttle (WOT) or when the ignition is ON while the engine is OFF. Under these conditions, the ECM uses the SCIAP sensor to determine the current BARO. The lowest manifold pressures occur when the vehicle is idling or decelerating. SCIAP can range from 8-10 kPa, when pressures are low, to as much as 207 kPa when pressures are high, depending on the BARO. The ECM monitors the SCIAP sensor signal for pressure outside of the normal range.