P0401 Buick - Exhaust Gas Recirculation Flow Insufficient
- Faulty EGR Valve
- EGR solenoid valve harness is open or shorted
- EGR solenoid valve circuit poor electrical connection
1997 Buick Century EGR Port Cleaning
User Submitted Video
- Possible engine hesitation
The Powertrain Control Module (PCM) tests the EGR system during deceleration by momentarily commanding the EGR valve open. The pressure in the intake manifold increases when the EGR valve is open. The PCM monitors the Manifold Absolute Pressure (MAP) sensor signal during the EGR system diagnostic in order to determine the amount of EGR flow. The PCM calculates an error based on the difference between the actual MAP increase and a predetermined value. The PCM records the error and adjusts an internal fail counter towards the fail threshold if the error is too great.