Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation Valve:

The EGR is used to lower oxides of nitrogen (NOx). By lowering combustion temperatures less NOx is formed.

A vacuum operated valve on the intake manifold allows a controlled amount of exhaust gas into the intake air.

At idle little or no EGR gas is passed because the exhaust gas will not burn and stalling or poor running would result.

This vehicle uses a positive backpressure valve and can be identified by the letter P stamped at the end of the part number. The valve is actuated by a pulse width modulation (PWM) solenoid that is controlled by the ECM. Inside the valve is an air bleed valve that acts as a vacuum regulator. The air bleed vents vacuum to the atmosphere. As pressure builds up in the exhaust the air bleed closes and the available vacuum from the PWM solenoid opens the EGR valve. Because of the air bleed system the valve will not open by applying vacuum with the engine stopped or at idle.