Trouble codes › P0401

P0401 Exhaust Gas Recirculation "A" Flow Insufficient Detected

Emissions

P0401 means the EGR system isn't flowing enough exhaust back into the intake, usually from carbon-clogged passages or a stuck valve.

The EGR system feeds a small amount of exhaust back into the intake to lower combustion temperatures and emissions. The engine computer opened the EGR valve and didn't see the change it expected (usually in manifold pressure or temperature), so it decided too little exhaust is flowing.

Can I keep driving? Yes, but get it fixed soon.

Usually drivable, but expect possible pinging (spark knock) under load and higher emissions. Fix it soon; ongoing knock can damage the engine.

Common causes

  1. Carbon buildup clogging the EGR passages (very common)
  2. A stuck or failing EGR valve
  3. A failed EGR vacuum solenoid or a cracked vacuum hose (on vacuum-operated valves)
  4. A faulty EGR position or pressure feedback sensor (DPFE sensor on many older Fords)

Symptoms

  • Check-engine light
  • Pinging or knocking when accelerating or climbing hills
  • Failed emissions test (high NOx)

What to check first

  1. Check the vacuum hoses to the EGR valve and its solenoid for cracks or disconnections.
  2. Remove the EGR valve and look for heavy carbon in the valve and the passage it feeds; cleaning the passages often fixes P0401.
  3. On electronic EGR valves, a scan tool can command the valve open: the idle should stumble when it opens.
  4. On older Fords, test or replace the DPFE sensor and its hoses (a common cause).

What does P0401 mean on your vehicle?

The likely cause depends on your engine. iRepair researches your exact year, make, model and engine (service bulletins, recalls and owner reports) and tells you what to check first. Your first 3 questions are free.

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Related codes

General guidance for P0401 on most vehicles. Some makers use the same code a little differently; confirm in the service information for your vehicle, put safety first, and see a professional when in doubt.