Have you also checked/replaced the EGR vacuum regulator solenoid and clean the back pressure transducer tubes along with their ports and the manifold tube?
DTC Code: P0401 Description: Exhaust Gas Recirculation Flow Insufficient Detected Probable Causes:
DTC Code: P0401 Description: Exhaust Gas Recirculation Flow Insufficient Detected Probable Causes:
- Sensor or solenoid faulty
- Connector terminal contact is damaged or corroded
- Wire harness - Check harness for correct voltage, open, short to ground or short to voltage
- Update control unit software - Check for the latest control unit update
- Powertrain or Engine Control Module faulty
- Exhaust leaks or restrictions
- EGR components clogged, dirty or leaky
- EGR valve damaged/defective