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 Switching Valve (VSV), which is controlled by ECM. Vacuum source to EGR VSV is controlled by Vacuum Control Valve (VCV). Amount of EGR valve opening is monitored by EGR valve position sensor, which is mounted on EGR valve.

EGR valve is closed (EGR VSV is on) when engine is not warmed up, vehicle is decelerating, engine is under light load, engine is speed more than 4000 RPM or when engine is idling. DTC is set when EGR cut-off, lift amount of EGR valve is .1" (2.6 mm) or more. Possible causes are:

• EGR valve is stuck open.
• Defective EGR VSV.
• EGR VSV circuit is open or shorted.
• EGR valve position sensor circuit is open or shorted.
• Defective EGR valve position sensor.
• Defective ECM.