Powertrain, generic · Auxiliary emission controls

P0401 EGR A Flow Insufficient Detected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. P0401 means too little exhaust is recirculated. Petrol engines open the valve briefly and expect a rise in manifold pressure (GM 2004 V6, MIL on the first trip); older Ford systems measure the pressure drop across an orifice (DPFE sensor). Diesels balance the air mass: if the meter sees more fresh air than the target EGR rate allows, too little exhaust flows (GM, Ford, Saab, usually MIL after two trips). Diesel causes are mostly a coked valve or cooler, petrol causes blocked passages.

Likely causes

EGR passages, valve or cooler carboned up
EGR valve faulty or stuck closed
Ford: DPFE sensor or its hoses blocked, cracked or swapped
Diesel: air mass meter drifting or air leak after the turbo
Vacuum control of the valve faulty

Symptoms

  • Check engine light on
  • Pinging or knocking under load (petrol)
  • Higher NOx, emission test failed
  • Often no noticeable symptoms

Repair estimate

DifficultyMediumDIY possible
Parts and labour€100–900
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Clean EGR passages
  2. Check valve movement
  3. Check position feedback

Parts involved

egr valveegr passagesegr coolerdpfe sensor

Related codes

P0400P0402P0404P042EP2457P0101

References: gsi.ext.gm.com, newtonnet.co.uk, fordservicecontent.com, gsi.ext.gm.com.