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 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 racing.

Code is set when EGR gas temperature sensor value does not exceed 72°F (40°C) more than ambient air temperature after vehicle is operated for 3-5 minutes (50 MPH or more). Possible causes are:

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