EGR Control Solenoid: Description and Operation

Wiring Diagram:

OPERATION:
The Powertrain Control Module (PCM) controls the vacuum to the Exhaust Gas Recirculation (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 which controls 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 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.

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 engine speed, the PCM 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 EGR.

The PCM uses the following sensors to control the EGR solenoid:

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