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 up to 12 EGR flow test counts during the first ignition cycle following a code clear event. Between 9-12 EGR flow test counts should be sufficient for the PCM to determine adequate EGR flow and pass the EGR flow test. If the PCM detects an EGR flow error, DTC P0502 sets.