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 temperature sensor value does not exceed ambient air temperature by more than 95°F (35°C) after vehicle is operated for 3-5 minutes at 50 MPH or more. Possible causes are:

• EGR valve is stuck closed.
• EGR VSV circuit is open.
• Defective EGR VSV.
• Defective vacuum control valve.
• EGR temperature sensor circuit is open.
• Defective EGR temperature sensor.
• EGR vacuum hose is disconnected.
• Defective ECM.