DTC P0401: EGR System Insufficient Flow: Description

Powertrain Control Module (PCM) tests Exhaust Gas Recirculation (EGR) system during deceleration by momentarily commanding EGR valve to open while monitoring Manifold Absolute Pressure (MAP) senor signal. When EGR valve is opened, PCM should see a proportional increase in MAP. If expected increase in MAP is not seen, PCM notes amount of error that was detected and adjusts an internal fail counter toward a fail threshold level. When fail counter exceeds fail threshold level, PCM will set this DTC. Number of test samples required to accomplish this may vary according to amount of detected flow error.

Normally, PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, PCM allows 12 test samples during first ignition cycle following a scan tool CLEAR INFO. Between 9 and 12 samples should be sufficient for PCM to determine adequate EGR flow and pass EGR test.