GM Service Manual Online
For 1990-2009 cars only

The EVO/Passlock module supplies a 5.0 volt reference and a ground circuit to the steering handwheel speed (HWSS) sensor. The HWSS returns a voltage signal to the EVO/Passlock module indicating the steering wheel rate of steer. The HWSS returns a voltage greater than 0.2 volts and no more than 4.9 volts when the steering wheel has been turned one quarter revolution (90 degrees). The EVO/Passlock module uses the sensor signal in order to control a percentage duty cycle (PWM) current to the steering assist control solenoid. The steering assist control solenoid, in turn, regulates the power steering pump output flow. Regulation of the steering pump output flow increases or decreases the power steering assist.