A 95% of P0401 cases stem from uncleaned carbon deposits in the intake manifold. Follow this protocol:
1. Remove EGR valve and thoroughly clean manifold channels with Liqui Moly Pro-line EGR Cleaner (penetrate 10cm deep)
2. Perform ECU reset: Clear codes and run 'EGR Adaptation Learn' (For Ford IDS: Toolbox > Powertrain > EGR Learn)
3. If unresolved, check EGR cooler blockage (airflow resistance must be <2.5 kPa)