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Enter a 5-character code such as P0420, P0301, or P0457.

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Codes starting with P are engine and transmission, B are body, C are chassis, and U are network communication. A 0 as the second character means a generic code shared by all makes; a 1 means a manufacturer-specific code, so its meaning depends on your brand.

A steady check engine light usually means get it checked soon. A flashing check engine light means an active misfire: reduce speed and stop driving as soon as it is safe.

That doesn't look like an OBD-II code

A valid code is one letter (P, B, C, or U) followed by four characters, for example P0420.

P0401 Exhaust gas recirculation (EGR) flow insufficient

Can I drive with P0401?

Drive

Safe to keep driving normally. Fix it when convenient.

Usually drivable, but you may hear pinging under load and the car can fail an emissions test. Ongoing pinging can damage pistons over time, so use the recommended fuel grade and avoid heavy loads until it is fixed.

What does P0401 mean?

Not enough exhaust gas is being recirculated into the engine, which raises combustion temperatures. The EGR system feeds a little exhaust back into the intake to cool combustion and cut nitrogen oxide emissions. The computer tests it by opening the valve and watching for a pressure or temperature change.

What causes P0401?

Carbon buildup is the most common cause, especially on high-mileage engines. Cleaning often fixes it without new parts.

  1. EGR passages clogged with carbon
  2. Stuck EGR valve
  3. Faulty EGR position or pressure (DPFE) sensor
  4. Leaking vacuum hose on older vacuum-controlled valves

How much does it cost to fix P0401?

$150 – $800

Passage cleaning: $150–$400. EGR valve: $250–$700. On many cars you can remove the valve and scrape carbon from it and its port yourself. Clean first, because a new valve on clogged passages soon sets the code again.

What are the symptoms of P0401, and how can I confirm it?

Pinging or knocking when accelerating or climbing hills is the main sign, though many cars show only the light. Remove the EGR valve and look for heavy carbon in it and its port. On a scan tool, commanding the valve open at idle should make the engine stumble. P0402 means too much flow instead.

Will P0401 fail an emissions test, and should I clear it?

It fails any OBD-II based inspection while the light is on, and low EGR flow raises nitrogen oxide emissions. After cleaning or a repair, clear the code and drive normally, including steady highway speeds, so the EGR monitor can run. If P0401 returns, carbon or a bad sensor remains.

Confirm the code yourself

A low-cost scanner lets you read the code, clear it, and see if it comes back before paying for a diagnosis.

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