Exhaust Gas Recirculation: Operation: Operation

An EGR valve assembly is located toward the front of the engine. An EGR solenoid, located on top of the intake manifold near EGR valve. The EGR solenoid controls the "on time" of the EGR valve. The Powertrain Control Module (PCM) operates the EGR solenoid. The vacuum pump supplies vacuum for the EGR solenoid and the EGR valve. This pump also supplies vacuum for operation of the power brake booster and the heating and air conditioning system. The pump is located in the rear of the cylinder head and is driven by the exhaust camshaft. When the PCM supplies a variable ground signal to the EGR solenoid, EGR system operation begins. The PCM will monitor and determine when to supply and remove this variable ground signal. This will depend on inputs from the engine coolant temperature, throttle position and engine speed sensors. When the variable ground signal is supplied to the EGR solenoid, vacuum will be allowed to pass through the EGR solenoid and on to the EGR valve through a connecting hose.

Exhaust gas recirculation will begin in this order when:

• The PCM determines that EGR system operation is necessary.
• The engine is running to operate the vacuum pump.
• A variable ground signal is supplied to the EGR solenoid.
• Variable vacuum passes through the EGR solenoid to the EGR valve.
• The inlet seat (poppet valve) at the bottom of the EGR valve opens to dilute and recirculate exhaust gas back into the mixing chamber.

The EGR system will be shut down by the PCM after 60 seconds of continuous engine idling to improve idle quality.