Circuit Description
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The Engine Control Module (ECM) opens the throttle blades by applying a pulse width modulated voltage to the throttle valve motor. The ECM reverses the polarity on the throttle valve motor control circuits in order to close the throttle blades. The ECM increases the pulse width as necessary to open the throttle blades. The ECM monitors the Throttle Position (TP) sensors 1 and 2 to determine the actual blade position. If the ECM detects the required Pulse-Width Modulation (PWM) to move the throttle blade exceeds a predetermined value, DTC P0638 sets.