P0401- Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

P0401 is defined as follows, Exhaust Gas Recirculation (EGR) Flow Insufficient Detected. This guide is designed to help you understand what this code means, what causes it to set and how it may be repaired.

To learn more about P0401 and what it means if you find this code, check out our guide below:

What is Code P0401?

The reason there is an Exhaust Gas Recirculation (EGR) system equipped on a vehicle is to cut the levels of Nitrogen Oxide (NOx) emitted by the engine. These gases are caused when the engine reaches high combustion chamber temperatures.  

As a result, the EGR plays a large part in cooling the combustion process by introducing inert gases back into the intake. But if the Exhaust Gas Recirculation (EGR) valve is defective or faulty, the Engine Control Module (ECM) may set a code to alert you.

By detecting various engine sensors and related systems the ECM can detect if the EGR valve has encountered a fault. If it detects to little flow of exhaust gases into the intake, it will set code P0401

P0401: Symptoms

P0401 code symptoms indicate a faulty Exhaust Gas Recirculation (EGR) system that is not flowing enough exhaust gases into the intake. Following are some signs of P0401 code:

  • Reduced acceleration
  • Check Engine Light is illuminated
  • Poor fuel economy
  • Rough Idling
  • Emission test failure
  • Pinging

These symptoms can cause serious damage to your vehicle. If you have P0401 make sure you diagnose and repair the issue as soon as possible.

What causes P0401?

A P0401 error can be caused by the following:

  • Blocked EGR tube
  • Damaged exhaust gas recirculation device
  • Defective differential pressure sensor
  • Wiring damage (damaged wiring or loose connections)
  • Powertrain Control Module (PCM)
  • Carbon build-up in EGR valve
  • Vacuum line faults, damaged lines, etc.

How to Fix the Error Code P0401?

Fixing error code P0401 can be done in various ways but figuring out what’s causing it is a little more challenging for someone who isn’t acquainted with it.

However, if you are confident to repair the problem yourself, you can consider following these steps.

Test for proper vacuum supply at the EGR valve if it is vacuum operated. If the PCM commands the EGR valve on and there is no vacuum it will assume the EGR is not functioning correctly.

If you have a linear EGR you will need a scan tool capable of bi-directional communications for the next step. Remove the EGR valve and re install the electrical connector.

Command the EGR valve open and closed while monitoring the position of the EGR pintle. If the EGR pintle does not move, you will need to inspect for cause of concern. Most likely this is caused by some sort of electrical failure.


Can I drive my vehicle with P0401?

Technically, you can drive your vehicle even when it has error code P0401. It will not cause any harm unless the vehicle starts running roughly.

There will be a few concerns that you will notice. The vehicle will run rough and also fuel economy will be reduced.

Pinging can also be a symptom of a faulty EGR valve and if this occurs internal engine damage can occur.

So our suggestion on this one is to get it fixed sooner than later.

Repair Costs

The cost of resolving the issues of the P0401 code depends on the components affected. Repair costs of some of the more typical repairs:

  • EGR valve replacement $300-$1500
  • EGR wiring repair $150-$300
  • EGR Differential pressure sensor $150-$250

P0402 is another code that is very similar. However, the major difference is P0402 sets when the PCM detects the Exhaust Gas Recirculation Valve has too much flow detected.

Thanks for taking the time to read this guide, we wish you the best of luck in your repairs. If you have any suggestions or want to let us know how you made out with your repair.

Please leave us a comment.

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