DTC P0401: EGR System - Insufficient Flow: Description

WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Powertrain Control Module (PCM) tests Exhaust Gas Recirculation (EGR) system during deceleration by momentarily commanding EGR valve open. pressure in intake manifold increases when EGR valve is open. PCM monitors Manifold Absolute Pressure (MAP) sensor signal during EGR system diagnostic to determine amount of EGR flow. PCM calculates an error based on the difference between actual MAP increase and a predetermined value. PCM records error and adjusts an internal fail counter towards fail threshold if error is too great. PCM sets this DTC when fail counter exceeds fail threshold. Number of test samples required to exceed fail threshold varies according to magnitude of detected flow errors. PCM allows only one EGR flow test sample to be taken during an ignition cycle. Following a scan tool CLEAR INFO or a battery disconnect, the PCM allows more than one sample per ignition cycle until 13 samples have been obtained in order to aid in verifying a repair.