DTC P1656: WASTEGATE Solenoid Control Circuit: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
The turbocharger wastegate is a vacuum actuated valve which is used in order to control the exhaust gas heat which is sent to the turbo. The wastegate Pulse Width Modulated (PWM) solenoid meters the vacuum level at the wastegate valve actuator as commanded by the Powertrain Control Module (PCM). When the PCM is commanding the wastegate solenoid ON, the voltage potential of the circuit will be low, near 0 volts. When the PCM is commanding the wastegate solenoid OFF, the voltage potential of the circuit will be high, near the battery voltage. The primary function of the PCM in this circuit is to supply the ground for the wastegate solenoid.