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.

EGR valve is closed (EGR VSV is on) when engine is not warmed up, vehicle is decelerating, engine is under high load, engine speed is more than 4000 RPM or when engine is idling. DTC is set when, after engine is warmed up, intake manifold absolute pressure is more than value calculated by ECM while EGR system is on. Possible causes are:

• EGR vacuum hose is disconnected.
• EGR Vacuum Switching Valve (VSV) circuit is open or shorted.
• Defective EGR Vacuum Switching Valve (VSV).
• EGR system malfunction.
• Defective EGR vacuum modulator.
• EGR valve stuck closed.
• Defective Manifold Absolute Pressure (MAP) sensor.
• Defective ECM.