DTC P0404: EGR Valve Open Pintle Position: Description
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Suburban, and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) monitors the EGR position sensor parameter of the Exhaust Gas Recirculation (EGR) valve to ensure that the valve responds properly to commands from the PCM. The PCM compares the EGR position sensor parameter with the desired EGR position parameter when the valve is commanded open. If the PCM detects a difference of 12 percent between the EGR position sensor parameter and desired EGR position parameter for a calibrated amount of time, DTC P0404 will set.