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P0401 — Exhaust Gas Recirculation Flow Insufficient Detected

moderate

What it means

The engine control module opened the EGR valve but the measured recirculation flow stayed below the expected value. Flow is judged either by the DPFE differential pressure sensor, by the EGR temperature sensor, or by the drop in intake manifold pressure when the valve is commanded open. Typical signs are pinging or knocking under load, slight loss of power and a failed emissions test because of high NOx.

Likely causes (most common first)

  1. Carbon deposits blocking the EGR valve seat and the recirculation passages in the intake manifold
  2. EGR valve stuck closed or seized
  3. Clogged, cracked or disconnected DPFE hoses; faulty differential pressure sensor
  4. Blocked EGR cooler or EGR pipe (common on diesels)
  5. Faulty EGR temperature sensor
  6. Vacuum leak or defective vacuum solenoid on vacuum-operated valves

Can you drive with it?

You can keep driving, but repair it soon: insufficient EGR flow leads to detonation under load.

This is the generic meaning. What about your car?

The same code has different typical culprits on different engines. Tell the AI your make, model and year — it will rank the causes for your exact car and give you a check order.

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