Circuit Description

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

The EGR valve is closed (VSV on) under the following conditions:

• Engine is not warmed up.
• Vehicle under deceleration.
• Light engine load.
• Engine racing.

DTC is set when EGR temperature sensor value does not exceed ambient air temperature by more than 140°F (60°C) after vehicle is operated for 3-5 minutes (50 MPH or more). Possible causes are:

• EGR valve stuck closed.
• VSV short circuit.
• EGR temperature sensor open circuit.
• EGR vacuum hose disconnected.
• ECM.