Circuit/System Description

The manifold absolute pressure (MAP) sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The engine control module (ECM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit, and provides a ground on the low reference circuit. The MAP sensor provides a voltage signal to the ECM on the signal circuit relative to the intake manifold pressure changes.

The sensor used on this engine is a three atmosphere sensor. Pressure in the intake manifold is affected by engine speed, throttle opening, turbocharger boost pressure, intake air temperature (IAT), and barometric pressure (BARO). Under normal operation the greatest pressure that can exist in the intake manifold at ignition ON, engine OFF is equal to the BARO. When the vehicle is operated at wide-open throttle (WOT), the turbocharger can increase the pressure to near 240 kPa. The least manifold pressure occurs when the vehicle is decelerating and can range from 13-48 kPa.

The purpose of this diagnostic is to analyze the performance of the MAP sensor by comparing the measured pressure changes to the following 2 distinct models:

• The engine cranking model uses BARO and boost pressure as inputs
• The engine running model uses BARO, boost pressure, throttle opening and engine speed as inputs