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P0401 – Meaning, Causes, Symptoms, & Fixes


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What Does Code P0401 Mean?

  • P0401 definition: Exhaust Gas Recirculation (EGR) Flow Insufficient Detected
  • Issue Severity: MODERATE – Extended driving with this code may cause internal engine damage.
  • Repair Urgency: Get this code fixed as soon as possible to avoid internal engine damage.
  • Diagnosis: Code P0401 can cause excessive internal engine ignition and pre-ignition damage to the pistons and valves. Use the FIXD Sensor and app to see the most likely fix and cost for P0401, get detailed diagnostics in plain English, access our Mechanic Hotline, and more.
  • Common Reason: Code P0401 is often related to an exhaust gas recirculation valve failure.

The exhaust gas recirculation (EGR) valve recirculates small amounts of exhaust back into the combustion chambers of the engine in order to decrease the amount of oxygen and increase the water vapor content, thereby reducing the formation of smog-producing nitrogen oxides (NOx). When the trouble code P0401 is set, exhaust gases are reintroduced to the combustion chamber at the incorrect time or in incorrect amounts, which does not decrease the oxygen level enough to prevent the increase of NOx. This is likely due to a faulty or clogged EGR valve or carbon buildup in the intake manifold or on the EGR temperature sensor.

P0401 Causes

There are many potential causes of code P0401.

  • Clogged or restricted EGR passages due to excess carbon
  • Faulty EGR valve
  • EGR temperature sensor is covered with carbon

P0401 Symptoms

  • Check Engine Light
  • Failed emissions test
  • Slower acceleration
  • Loss of power
  • Ignition pinging

How Do I Fix Code P0401?

With an EGR fault, the first step is to get it diagnosed to figure out what is causing the problem.

The FIXD Sensor and app can help you diagnose and fix P0401 yourself by giving you access to detailed engine diagnostics that are easy to understand (even if you don’t know cars), live OBD2 data, and a Mechanic Hotline. You can even use FIXD to clear the fault codes on your vehicle and see if your fix worked, or simply turn off codes that aren’t serious.

> Click here to get FIXD for $19.99 for a limited time!

If your vehicle has this fault and you’re not comfortable diagnosing this issue at home, we recommend finding a RepairPal certified shop nearby to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

How Much Does It Cost to Fix Code P0401?

P0401 can be caused by anything from a clogged EGR valve to a faulty EGR temperature sensor to an engine vacuum leak. It’s impossible to give an accurate estimate without properly diagnosing the issue first. 

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0401 code.

Possible Repair Costs for P0401

For error code P0401, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.

  • EGR valve: $332 to $413
  • Vacuum leak: $90 to $125

DIY Steps to Diagnose Code P0401

Engine code P0401 could be caused by a number of things, including a clogged EGR valve, a faulty EGR temperature sensor, or an engine vacuum leak. If you’d like to try to fix code P0401 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Keep in mind this is an intermediate-level diagnosis and repair and not recommended for beginners. Diagnosis requires more specialized equipment beyond what the FIXD Sensor can provide and it can be a time and labor-intensive process for inexperienced DIYers.

DIY difficulty level: Intermediate

This repair requires mechanical knowledge and is not recommended for beginners.

Tools/parts needed (our top picks from Amazon):


Use your car’s service manual to locate and check the EGR valve for any carbon buildup. Check out this video for a visual reference. If you find carbon buildup, use a speedometer cable and throttle body cleaner to remove carbon blocking any air passages. Use FIXD to clear your check engine light. Go for a test drive and see if the check engine light turns back on.


Use your car’s service manual to locate and check the vehicle’s EGR temperature sensor for any carbon buildup that may interfere with its readings.


Visually inspect the vacuum hoses, wiring, and any other connections to the EGR valve that may interrupt airflow to the intake manifold. If you find damages or cracks in any of these connections, replace the defective parts and use FIXD to clear your check engine light.


Use your car’s service manual to locate and remove the intake manifold to check for carbon build-up. Check out this video for a visual reference. 

Remove all hoses connected to the intake. Remove the air intake hose that is connected to the throttle body. Remove the throttle body. Remove the intake manifold and inspect it for carbon buildup. If it needs cleaning, use a speedometer cable and throttle body cleaner to remove carbon buildup as you did on the EGR valve. Reinstall the intake manifold and reconnect the hoses, throttle body, etc.

If these steps do not clear your Check Engine Light, you may need to visit a mechanic because there may be a vacuum leak or internal electrical issues.

Common P0401 Diagnosis Mistakes

Replacing the EGR valve without trying to clean it first.

Still Need Help Fixing Code P0401?

If you’ve followed the steps above and are still experiencing check engine code P0401, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price. Don’t have a FIXD Sensor yet? Click here to get yours for just $19.99, including a free 14-day trial of FIXD Premium!

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Fixed It But The Check Engine Light Is Still On?

Check engine light sometimes need to be reset manually, check out our article:

How to Reset Your Check Engine Light | 4 Ways To Clear It (With or Without a Scanner)

Justin Hughes

Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

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About the Author

Justin Hughes

Justin Hughes

Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

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