Circuit Description

EGR system recirculates exhaust gas through intake system to reduce combustion temperature and NOx emissions. Amount of EGR valve opening is regulated by EGR vacuum modulator according to engine load. Vacuum source to EGR valve is controlled by EGR Vacuum Switching Valve (VSV), which is controlled by ECM.

The EGR valve is closed (VSV on) when engine is not warmed up, vehicle under deceleration, engine idling, high engine load or engine speed more than 4400 RPM. DTC is set when engine is warmed up, and intake manifold absolute pressure is more than value calculated by ECM while EGR system is on. DTC will also set if a misfire is detected during idling. Possible causes are:

• EGR valve is stuck open.
• Defective EGR Vacuum Switching Valve (VSV).
• EGR VSV circuit is open.
• Defective Manifold Absolute Pressure (MAP) sensor.
• Defective EGR vacuum modulator.
• Defective ECM.