EGR Control Solenoid: Description and Operation

Wiring Diagram:

SYSTEM OPERATION
The Powertrain Control Module (PCM) controls the vacuum to the EGR valve with a solenoid valve. A constant ignition voltage is applied to the positive terminal of the EGR solenoid. The vacuum supply to the EGR valve is regulated by the PCM which controls the ground to the EGR solenoid.

SOLENOID DUTY CYCLE
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 the EGR valve (turn EGR full "ON") since a de-energized solenoid allows vacuum to pass to the EGR valve. A duty cycle of 100% will turn the EGR valve full "OFF" since the solenoid will be energized and will not allow vacuum to flow to the EGR valve.

EGR CONTROL
The EGR duty cycle is regulated by the PCM depending on engine load conditions. When the engine is cold, within a specified load range, and above a specified engine speed, 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 signal to the solenoid to allow the EGR to operate.

SENSOR INPUTS
The PCM uses the following sensor inputs to control the EGR solenoid:

^ Engine Coolant Temperature (ECT) Sensor.
^ Throttle Position (TP) Sensor.
^ Manifold Absolute Pressure (MAP) sensor.
^ Intake Air Temperature (IAT) sensor.
^ Engine speed data from distributor reference pulses.
^ Vehicle Speed Sensor (VSS).