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 Switching Valve (VSV), which is controlled by the ECM. Vacuum source to VSV is controlled by the Vacuum Control Valve (VCV). Amount of EGR valve opening is monitored by the EGR position sensor, which is mounted on EGR valve.

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

• Engine is not warmed up.
• 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 ambient air temperature by more than 104°F (40°C) after vehicle is operated for 3-5 minutes (50 MPH or more). Possible causes are:

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