EGR Valve Description

Exhaust Gas Recirculation:

Positive Backpressure EGR Valve:

EGR VALVE
This vehicle uses a positive backpressure EGR valve. A positive backpressure EGR valve requires exhaust backpressure (proportional to engine flow) to open and allow exhaust gas to flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, the engine might misfire. For this reason, very little exhaust gas is allowed to pass through the valve, especially at idle. Careful diagnosis of the system is important so that outside conditions (such as an exhaust tube connected to the vehicle causing reduced exhaust backpressure) will not lead to misdiagnosis.

The EGR valve is usually open under the following conditions:

^ Warm engine operation.
^ Above idle speed but below wide open throttle.

EGR SOLENOID OPERATION
The PCM controls the vacuum to the 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 controlling the ground to the EGR 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 EGR (turn EGR full "ON") since a de-energized solenoid allows vacuum to pass to the EGR valve. A duty cycle of 100% will turn EGR full "OFF" since the solenoid will be energized and will not allow vacuum to pass to the EGR valve.

EGR PULSE WIDTH
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 RPM, 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 duty cycle to the solenoid to allow EGR operation.