DTC P0401: Insufficient EGR 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) sensor signal. When EGR valve is opened, PCM should see an increase in MAP. If expected increase in MAP is not seen, PCM notes amount of error detected and adjusts an internal fail counter towards a fail threshold level. When fail counter exceeds fail threshold level, PCM will set DTC.

The number of test samples required to accomplish this may vary according the amount of detected flow error. Normally, PCM will only allow 1 EGR flow test sample to be taken during an ignition cycle. PCM allows 12 test samples during first ignition cycle following a scan tool CLEAR INFO command or when battery is disconnected and reconnected. Between 9-12 samples should be sufficient for PCM to determine adequate EGR flow and pass EGR test.