P0401 Code – Meaning, Causes, Symptoms (& How To Fix)

Wondering what that P0401 code means on your code scanner? This article tells you everything you need to know, from causes and symptoms to fixes.

P0401 Code

When the Check Engine Light comes on, the fault could be any number of problems. That’s why it’s important to investigate the problem with your code scanner. If your OBD-II scanner shows the P0401 code, you can fix it without a lot of experience.

In this guide, we evaluate what the P0401 trouble code means and the symptoms it leads to. We also examine the various causes, so you can determine how to fix it. 

Code P0401 Definition

P0401 – Insufficient Exhaust Gas Recirculation (EGR) Flow

What Does the P0401 Code Mean?

P0401 is a generic trouble code indicating that the engine control module (ECM) noticed the engine exhaust gas recirculation (EGR) valve isn’t moving the right amount of recirculated gases. This fault occurs when the EGR valve is meant to allow gases to flow into the intake manifold. 

The EGR valve is used to recirculate a particular amount of exhaust gas back to the engine’s combustion chambers, thereby decreasing the water vapor and oxygen content. With this design, nitrogen oxide gases are reduced. However, the P0401 code shows that the exhaust gases aren’t recirculating as they should, so there could be an increase in NOx. 

P0401 Trouble Code Symptoms

In many cases, the first sign that something is wrong is when the Check Engine Light comes on. Aside from this symptom, there could be other problems present. 

Here are a few you could notice:

Causes of the P0401 Code

Because the P0401 trouble code corresponds with the EGR valve, most causes have to do with this vital component. However, there are other issues you could be looking at.

Here are the top causes of the P0401 DTC.

How Serious is the P0401 Code?

Medium – If all that’s wrong with your vehicle is the Check Engine Light, you might be tempted to continue driving it. While you might not experience any problems, it might not seem like a big deal to keep going until the repairs are more convenient for you.

However, it’s not good for the vehicle or the environment to run with the wrong emissions balance. On top of that, the vehicle might not pass an emissions test when the time comes. Instead, get the car looked at for a quick repair and more efficient operation. 

What Repairs Can Fix the P0401 Code?

It’s important that you walk through the complete P0401 trouble code diagnostic steps to figure out what’s wrong. Only after these steps have been taken can you determine what needs to be repaired.

However, these are the most common fixes you might encounter.

  • Clean EGR passages
  • Replace EGR valve
  • Replace the failing sensor (manifold absolute pressure, differential pressure, etc.)
  • Repair vacuum supply 
  • Repair loose connections or damaged wiring
  • Update/replace ECM

Common P0401 Diagnosis Mistakes

If you see the P0401 trouble code, your immediate reaction is to replace the EGR valve. That’s what makes the most sense to people but isn’t always the best option.

Instead, you want to make sure you are walking through all of the diagnostic steps. It’s possible that the sensor simply has carbon buildup on it that can be cleaned, thereby saving you a good amount of money. 

How to Diagnose the P0401 Trouble Code

With a few simple tools, you can diagnose the P0401 DTC at home, just like the professionals would. We outline some steps you might want to follow but also recommend that you stick to the advice found in your car’s service manual.

  1. Read all of the trouble codes. There could be other codes present that help you pinpoint the issue.
  2. Clean the EGR valve. With throttle body cleaner, you can remove any carbon buildup from the sensor and air passages. If reachable, sometimes the EGR valves can be very difficult to reach.
  3. Check all of the connectors and electric wiring for faults that need to be repaired.
  4. Check the vacuum to see if the airflow is interrupted. If there are any faults with the system, repair them. 
  5. Replace the EGR valve to see if that resolves the issue.

If the Check Engine Light still won’t go away, it’s best to visit a professional mechanic for more guidance. 

Estimated P0401 Repair Cost

Once you’ve walked through all of the diagnostic steps, you’ll have a better idea about what needs to be repaired. Depending on what you find, you might be looking at some of these approximate costs, which include both parts and labor.

  • Clean EGR passages – $65-$175
  • Replace EGR valve – $300-$450
  • Replace failing sensor – $220-$550
  • Repair vacuum supply – $125-$375 
  • Repair loose connection or damaged wiring – $50-$550
  • Update/replace ECM – $250-$2,500

Mechanics Tips about the P0401 Code

The P0401 trouble code gets triggered any time that the EGR temperature sensor doesn’t see the right balance of recirculated gas in the system. This is most often caused because the EGR doesn’t open when it’s commanded to.

Because of the heat coming from the EGR gases, the sensors are subject to an excessive amount of carbon buildup. This buildup can also collect within the EGR passages, which is why it’s imperative to clean the whole system if you notice a problem. You can use throttle body cleaner to get the job done quickly. 

Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.

Related Posts