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.

DTC is set when EGR temperature sensor value is high during EGR cut-off when engine is cold, or if EGR valve is always open. Possible causes are:

• EGR valve stuck open.
• VSV open circuit.
• EGR temperature sensor short circuit.
• ECM.