Check Engine Code P0401

What does P0401 code mean? Find what causes it and learn how to fix this check engine code from a mechanic who has done it countless times.

This trouble code "insufficient EGR flow" means that there is not enough exhaust gasses flowing back into the incoming air to the engine. EGR stands for "exhaust gas recirculation". The EGR system consist of three parts: EGR valve, DPFE (differential pressure sensor EGR) and actuator solenoid.

Car manufacturers created this system so already burned exhaust gas can flow back into the engine (when the EGR valve is open) and lower the combustion temperatures. This helps reduce emissions.

This OBD code basically means that the cars computer has tried to open the EGR valve, but it cannot get enough exhaust gas into the engine. EGR systems used to be controlled by engine vacuum via hoses and valves. Now most of them are controlled by electrical solenoids.

What Causes the P0401 Code?

EGR Valve
  • EGR Valve
  • Blocked EGR Passageways
  • EGR Control (No or Low Vacuum)
  • Faulty solenoid or wiring

Less Common Causes

  • The Cars Computer
  • DPFE (Delta Pressure Feedback EGR) Valve
  • Modulator Valve

To troubleshoot, repair and maintain your vehicle, you'll need diagnostic and repair information that is specific to your car or truck. For this I personally use and recommend ALLDATAdiy. With full manuals for over 30,000 vehicles online, you will find an exact match for your vehicle's year, make and model.

Besides being cheaper than a factory manual, they also offer step by step repair instructions and detailed diagrams beyond what is found in most printed manuals. Click here for a sample of their diagnostic and repair information.

How to Fix Engine Code P0401

Each car manufacturer has their own EGR system design but the most likely two causes of this code are the valve itself or passageways (many times the intake manifold will have very small passageways that get clogged with soot) that the exhaust gasses pass through.

Many times this code is caused by clogged EGR passages, and sometimes removing the sensor will give you access to the clogged EGR passages.

Another thing that you can do yourself is to check all vacuum hoses and all wiring going to the EGR valve. You might find a hose with a hole in it or you could find a connector that is not seated all the way or some wiring that has been rubbed through.

This fault code is a tougher one for a DIY mechanic to diagnose unless you have good experience and some specialized tools. Many times this code will go away if you replace the EGR valve (but not always). If you lack the skills or patience to diagnose this problem, you can consider giving it a shot and just replace the EGR valve.

If you still have any unresolved vehicle problems or questions, you can ask an auto mechanic online. For expert answers specific to your vehicle's make and model, I recommend JustAnswer Car. They have a large pool of certified mechanics to answer your questions for a small fee and you can also browse their answers to other users for free.

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