How to Fix a P0401 Code on Honda Accord (Step by Step – Solved!)

P0401 Code honda accord

Do you know how to fix a P0401 code (Exhaust Gas Recirculation Insufficient Flow) on Honda vehicles? this is one of the questions our readers ask a lot. Well, we´ve got you covered.

Sometimes you may notice that the check engine light is on while the engine is not very smooth nor economic.

You could start hearing a knocking sound when starting up, or the engine’s RPM going up and down on the upper rev range during the ride.

In addition to this, you could notice a decrease in fuel economy with an increase in the temperature of the engine.

This could motivate you to get the codes read, and the P0401 could be stored in the ECM.

To quickly fix the P0401 code on Honda vehicles, you need to follow the steps below:

  • Step #1 Check EGR valve
  • Step #2 Check EGR pipe
  • Step #3 Check EGR ports/passages

Meaning: What is the P0401 Code on Honda Accord

The P0401code is one of the many standard OBD-II codes, and it stands for Exhaust Gases Recirculation Insufficient Flow Detected.

Exhaust Gas Recirculation, or EGR, is a system that decreases the amount of NOx generated during combustion.

Because NOx is produced at very high temperatures, EGR is used to lower the temperature of combustion.

The temperature of combustion depends on the volume of the fuel-air mixture, so exhaust gases are recirculated through the intake manifold.

Depending on the RPM range the engine is in, the ECM will control how much exhaust gases are recirculated.

At idle there will be no flow, but at high RPMs, there will be maximum flow.

If the engine detects that there is flow much lower than the predetermined level based on the RPM range, the P0401 code will be stored.

This situation will certainly lead to the engine overheating eventually, which can cause further damage to the engine.

So, fixing it is something you should do as soon as possible.

It is a relatively cheap problem to fix, though leaving it for some other day can be very expensive.

Read also: How To Fix P0304 Code For Honda Civic

Causes of the P0401 Code

When it comes to the causes of the P0401 code, on most motor vehicles it can be one or more of the multitude of things.

But when it comes to Honda Accord, it can be one or two things from three possible causes.

The P0401 means that the flow of recirculated gases is low because it is obstructed, or very rarely the EGR pipe is leaking.

The exhaust gases are never very clean, and when they pass through things, various products of combustion get deposited on surfaces.

This fouling can and will obstruct the passages through which the recirculating gases have to pass.

And this is something you can count on happening with time on any Honda Accord.

Places, where this carbon accumulation can cause problems, are the EGR valve plunger and ports, EGR tubes, and EGR plate and ports on the intake manifold.

With the EGR system, in general, there can exist a number of other issues.

But on Honda Accord they are handled by some other OBD-II codes, and the P0401 is almost always obstructed flow due to carbon buildup.

P0401 Honda Accord – How to Clean EGR Passage in V6 Engine >> Check out the video below:

Diagnosis: Reading P0401 Code

Just like for any other OBD-II code, to read it you will need some kind of OBD-II scanner.

You can use even those no-name cheap scanners that can be bought online for just a few bucks.

The type that connects to your mobile phone over the Bluetooth connection.

They are good enough, though the more expensive professional hand-held models will serve the purpose too.

The OBD-II port location on Honda Accord depends on the exact generation of the car.

On the sixth and earlier generations, it is located under the plastic cover on the left side from the cigarette lighter.

While on the seventh and newer ones it slightly varies, but it is in general on the underside of the dashboard, just above the trunk release lever.

To read the code, you will need to connect the OBD scanner to this port and scan for all codes.

Depending on what exact type and model of scanner you are using, this means that you will need to press or click on the Scan button in the scanner’s interface.

Scanning can take from few seconds to a minute or two, and the result will be shown on the display of your device.

Troubleshooting P0401 Code on Honda Accord (Step by Step)

Troubleshooting the P0401 code on Honda Accord comes down to checking all three possible places of carbon accumulation and cleaning them properly.

While there are other potential problems with the EGR, when it comes to code P0401 on a Honda Accord, it is almost always the carbon buildup obstructing the flow.

Step #1 Check EGR valve: On most of the Accord’s engines, the EGR valve is located just to the right from the oil dip-stick, and a little bit under.

To check it, you will need to remove it by disconnecting its harness and unscrewing two number 12 nuts that hold it.

When removing it, you should have in mind that to put it back you should use a new EGR valve gasket.

Once off, with nose pliers, you should pull the plunger on its underside, if it retracts easily then there isn’t much fouling of the plunger.

By visually inspecting the port next to it you can see whether it needs to be cleaned or not.

For cleaning both of these break cleaners and wire brushes do nicely.

Step #2 Check EGR pipe: Depending on the exact generation and engine model, the EGR pipe’s position and removal differ.

But, whichever is the proper procedure, you will need to check it for cracks and holes and clean it using a wire brush and carburetor or brake cleaner.

Step #3 Check EGR ports/passages: Cleaning the EGR ports and passages depends on whether it is an inline or V6 engine on your Honda Accord.

For inline engines you will need to remove the fuel rail, so you could reach the ERG plate and ports.

When removing the EGR plate, if you are gentle you will be able to reuse the gasket for it, otherwise, you will need a new one.

The plate is easiest to clean with a wire brush and carburetor or brake cleaner.

Under the plate, there are four ports that also need to be cleaned, which is a good idea to use a round wire brush and shop vac.

On the V6 engines, you will have to remove the intake manifold, as the ports are located on its underside, toward the throttle body.

You will also need to check and clean the port on the side of the intake, and it is a good idea to place some rags over the intake holes while doing it.

Prevent P0401 Code

If you are an owner of a Honda Accord, you can expect the P0401 code to happen once or twice during the lifespan of your car.

And you can be certain that the cause of it will be the carbon buildup in the valve, or passages. Sometimes the culprit can be even the EGR pipe, though it usually happens after 400,000 miles.

So, preventing the P0401 code comes down to cleaning the EGR ports and passages before they become clogged.

Normally it takes between 150,000 and 250,000 miles for them to get clogged, depending on the quality of fuel you are using and what detergents it has in it.

So cleaning it before this point will serve as prevention.

Repair Cost of P0401

Because the repair of code P0401 on the Honda Accord comes down to cleaning parts of the EGR system, most of the price is the labor.

It can range from $50 to $250 if everything needs quite a bit of cleaning.

A smaller part of the price is the gaskets that would need to be replaced, which range from $2-$3 for the EGR valve to $30-$35 for the EGR plate.


The P0401 code means that the recirculated exhaust gases are not flowing back into the intake manifold at the desired rate.

On Honda Accord this happens almost always because the passages through which exhaust gases flow are clogged by carbon buildup.

Fixing this problem or preventing it, comes down to cleaning three parts where such obstruction can develop.

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Jeff is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Reatta. Jeff has been creating written and video content about transportation, automotive, electric cars, future vehicles as well as new, used for more than 18 years. Jeff is based in Boulder, Colorado.

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