Circuit Description

The manifold absolute pressure (MAP) sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by engine speed, throttle opening, air temperature, and barometric pressure (BARO). A diaphragm within the MAP 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 MAP sensor wiring includes three 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 MAP sensor provides a signal voltage to the ECM, relative to the pressure changes on the MAP 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 the 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 MAP sensor to determine the current BARO. The lowest manifold pressures occur when the vehicle is idling or decelerating. The MAP can range from 10 kPa when pressures are low to as much as 104 kPa when pressures are high, depending on the BARO.

Within the ECM, the intake flow rationality diagnostic has the ability to determine an inaccurate input from the three systems it monitors. Calibrated within the diagnostic are estimates for the MAP, the mass air flow (MAF), and the throttle position (TP) for all engine operating conditions. The diagnostic compares the estimated values to the actual sensor inputs. If the ECM detects that the MAP sensor input is not within a calibrated limit of the estimated value, DTC P0106 sets.