Circuit/System Description

WARNING: This page is about a different car, the 2010 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.

The turbocharger incorporates a wastegate that is controlled by a pressure differential, that is determined by the engine control module (ECM) by means of a pulse width modulation (PWM) solenoid valve, in order to regulate the pressure ratio. A charge air bypass valve is integrated within the unit, and is also controlled by the ECM by utilizing a remotely mounted solenoid valve to prevent surging and damage from vibrations by opening during abrupt closed throttle conditions. When the bypass valve is commanded open during closed throttle deceleration conditions, the bypass valve allows the air to recirculate in the turbocharger and maintain speed. Within a calibrated range during the closed throttle event, or upon a wide open throttle command, the bypass valve will then close to optimize turbocharger response.

The purpose of this diagnostic is to determine if the charge air bypass valve is stuck closed. The ECM will first verify the integrity of the following sensors. The ECM then compares the actual measured mass air flow to a modeled airflow that is derived from these inputs:

The throttle position
The engine speed
Intake Air (Boost) Pressure and Temperature Sensor
Barometric Pressure (BARO)