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 122°F (50°C).
• Vehicle under deceleration.
• Light engine load.
• Engine idling.
• Engine racing.
• High engine load.

Code is set when intake manifold absolute pressure is greater than the value calculated by ECM while the EGR system is on. Possible causes are:

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