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 under deceleration, under light engine load or engine is racing. DTC is set when EGR temperature sensor value does not exceed ambient air temperature by more than 86°F (30°C) after vehicle is operated for 3-5 minutes (50 MPH or more). Possible causes are:

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