EGR System

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The EGR system is used to reduce the amount of Nitrogen Oxide (NOx) emission levels caused by combustion temperatures exceeding 1500°F (816°C). It does this by introducing small amounts of exhaust gas back into the combustion chamber. The exhaust gas absorbs a portion of the thermal energy produced by the combustion process and thus decreases combustion temperature. The EGR system will only operate under specific temperature, barometric pressure and engine load conditions in order to prevent driveability concerns and to increase engine performance.

The EGR valve is vacuum operated. Vacuum for the EGR valve control system is supplied by a belt driven vacuum pump. The EGR valve vacuum control solenoid and EGR valve vacuum vent solenoid work together to control the position of the EGR valve. ECM monitors EGR vacuum sensor signal to determine the amount of vacuum that is applied to EGR valve. The ECM uses the MAF sensor to calculate the amount of exhaust gas that is consumed by the engine. When EGR valve is opened, MAF rate will decrease. If EGR vacuum sensor signal is lower than desired and MAF rate is higher than expected, it is assumed that EGR valve is not opening enough due to a vacuum problem and a DTC will set.