Cutlass V6-260 4.3L DSL (1984)
EGR Vacuum Solenoid Valve: Description and Operation
EGR Solenoid
EGR valve operating vacuum is controlled by a Pulse Width Modulated (PWM) solenoid. Battery voltage is applied to the solenoid when the ignition
switch is in the on position, and the solenoid ground path is completed through the ECM. When the ECM completes the solenoid ground path, the
solenoid is ``on'' and vacuum is applied to the EGR valve. The ECM cycles the solenoid ``on'' and ``off'' at a constant rate, while vacuum is regulated by
varying the ``on'' time (dwell period) of each cycle from 0% to 100%. The ECM monitors EGR valve operating vacuum through the MAP sensor and
corrects variations between calculated and actual EGR by increasing or decreasing the solenoid dwell period. The ECM also detects vacuum system
malfunctions (leaks, blockage, etc.) through the MAP sensor, and if a malfunction is detected, the ``Check Engine'' lamp is illuminated and the EGR
solenoid is de-energized until the ignition switch is turned off.
