DTC P0404: EGR Valve Open Pintle Position: Description

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 Exhaust Gas Recirculation (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 the EGR valve vacuum vent solenoid work together to control the position of the EGR valve. The Engine Control Module (ECM) monitors the EGR vacuum sensor signal to determine the amount of vacuum that is applied to the EGR valve. The EGR throttle valve is used to create a restriction in the air intake in order to increase the engine vacuum. When the EGR valve is commanded to open, the EGR valve is commanded open, the EGR throttle valve is commanded to partially close. The increase in engine vacuum aids in the recirculation of the exhaust gases when the EGR valve is open. The ECM uses the mass air flow (MAF) sensor to calculate the amount of exhaust gas that is consumed by the engine. When the EGR valve is opened, the MAF rate will decrease. If the EGR vacuum sensor signal is lower than expected and the MAF rate is higher than expected, it is assumed that the EGR valve is not opening enough due to a vacuum problem and Diagnostic Trouble Code (DTC) P0404 sets.