Circuit Description

The EGR valve is controlled by an ECM-operated solenoid. The solenoid is normally closed and vacuum source is a ported signal. The ECM will turn EGR on and off (duty cycle) by grounding circuit No. 435. The duty cycle (on-off sequence) is calculated by ECM, based upon information from coolant temperature sensor, MAP sensor, and engine RPM. The duty cycle should be 0% (no EGR) when in Park or Neutral with TPS input below a specified value, or TPS indicating wide open throttle.