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 vacuum according to engine load. Vacuum source to valve is controlled by the Vacuum Switching Valve (VSV), which is operated by ECM.

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

• Coolant temperature less than 140°F (60°C).
• Vehicle under deceleration.
• Light engine load.
• Engine speed more than 4000 RPM.
• Engine idling.

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

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