P0401 – Meaning, Causes, Symptoms, & Fixes

Code P0401 Definition

Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

Code P0401 Meaning

The exhaust gas recirculation (EGR) recirculates small amounts of exhaust back into the combustion chambers of the engine in order to decrease the combustion temperature, thereby reducing the formation of smog-producing nitrogen oxides. EGR valves can malfunction by becoming stuck open or closed due to carbon buildup. When the trouble code P0401 is set, CO2 is reintroduced to the combustion chamber at the incorrect time or in incorrect amounts, which does not decrease the combustion temperature sufficiently enough to prevent the increase of NOx. This is likely due to faulty or clogged EGR valve or carbon buildup in the intake manifold or on the EGR temperature sensor.


  • Check Engine Light
  • Failed emissions test
  • Slower acceleration
  • Ignition pinging


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

Code P0401 Severity – Moderate   

Code P0401 can cause can cause excessive internal engine ignition and pre-ignition damage to the pistons and valves.

Code P0401 Common Diagnosis Mistakes

Replacing the EGR valve without checking the air passages of the intake manifold or the temperature sensor

Code P0401 Diagnosis Steps

How To Diagnose P0401

  1. Visually inspect the vacuum hoses, wiring, and any other connections to the EGR valve that may interrupt air flow to the intake manifold.
    1. If you find damages or cracks in any of these connections, replace and clear your check engine light
  2. 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
    1. Remove carbon using speedometer cable and throttle body cleaner
  3. Use your car’s service manual to locate and check the EGR valve for any carbon buildup.
    1. Check out this video for a visual reference
    2. If you find carbon buildup, use a speedometer cable and throttle body cleaner to remove carbon blocking any air passages.
  4. Use your car’s service manual to locate and remove the intake manifold to check for carbon build up.
    1. Check out this video for a visual reference
    2. Remove all hoses connected to the intake
    3. Remove air intake hose that is connected to the throttle body
    4. Remove throttle body
    5. Remove intake manifold to inspect for carbon buildup – use speedometer cable and throttle body cleaner to remove carbon buildup
    6. Place intake manifold back in and reconnect hoses, throttle body, etc.
  5. If these steps do not clear your Check Engine Light, you may need to visit a mechanic because there may be internal electrical issues.

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Comments 12

Dwayne Tant

July 11, 2018

Put egr value on check for any build up it had none but still tryed clean or clearing out but nothing it was clean at 141.000 miles and cleared light and week or little more it come back on still don’t know what to do next

FIXD Marketing

July 12, 2018

Hi Dwayne,

Have you checked the passages that go to and from the EGR valve? There may be some build up carbon there. If there is nothing there, you may need to take it to a mechanic, inform them of what you’ve already done and see what they can do.

Thank you,
The FIXD Team

david moore

July 21, 2018

is there a product on the market, (additive) that you can use to keep the carbon from building up and keep the egr valve from getting dirty in the first place?

FIXD Marketing

July 25, 2018

Hi David,

I am not currently aware of a product on the market that keeps carbon from building up. If you find one we would love to hear back from you!

Thank you,
The FIXD Team

david moore

September 27, 2018

I did take my car to a local mechanic, approximately a month ago They replaced the EGR valve, cost $820.00 Everything was good until recently, (yesterday). Then the check engine light came back on. I reinserted the FIXED sensor and the code came back P0401. The Suzuki Grand Vitarra is hard to start and has a bad miss when running.


September 19, 2019

Obviously the EGR valve was not your problem. I hope the mechanic who charged you that outrageous price for replacing a 125.00 EGR will now repair the problem without any more damage-to your wallet.

Jaime Pina

November 1, 2018

The coils are what was causing my issues for a longtime and finally got them done and now I’m getting the erg code po401 but at least it’s not cutting out and hesitating anymore so I would check them out

Adnan M.

January 5, 2019

Had the same code P0401. Check Engine Light was “on” for 4-6 months.
Put Techron Complete Fuel System Cleaner with gas, and the light was gone 🙂

Anthony V

February 17, 2019

Check engine light came on and two days later it shut off. The p0401 code is still in computer. Do I need to go further with a costly replacement or erase code and check to see if it comes on again.

nicole curry

July 3, 2019

I changed my egr valve but the check engine light is still on. Should it have gone off immediately after installing the new valve?


October 4, 2019

You would of had to delete the code with a diagnostic tool


September 10, 2019

Try Lucas fuel injector cleaner and upper cylinder lubricant. It has turned my P0401 code light off and stays off for weeks at a time. 236k miles on Toyota Camry.

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