Seville V8-300 4.9L (1991)
EGR Control Solenoid: Description and Operation
The PCM controls the vacuum to the EGR valve with a solenoid valve. A constant 12 volts is applied to the positive terminal of the EGR solenoid. The
vacuum supply to the EGR valve is regulated by the PCM controlling the ground to the EGR solenoid.
The percentage of time that the PCM grounds the EGR solenoid is called the solenoid duty cycle. The duty cycle is the time the solenoid is ON divided
by the time it is OFF. A duty cycle of 0% will enable EGR (turn EGR full on) since a de-energized solenoid allows vacuum to pass to the EGR valve. A
duty cycle of 100% will turn EGR full off since the solenoid will be energized and will not allow vacuum to pass to the EGR valve.
The EGR pulse width is regulated by the PCM depending on engine load conditions. When the engine is cold, within a specified load range and above a
specified RPM, the solenoid valve sends 100% duty cycle to the solenoid and blocks vacuum to the EGR valve. When the engine is warm, the PCM
sends a duty cycle to the solenoid to allow EGR operation.
