Auxiliary Emissions ControlOBD2 Codes

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.

Symptoms of Code P0401

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

Causes of Code P0401

  • 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. 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
  3. Remove carbon using speedometer cable and throttle body cleaner
  4. 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.
  5. 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
  6. Remove all hoses connected to the intake
  7. Remove air intake hose that is connected to the throttle body
  8. Remove throttle body
  9. Remove intake manifold to inspect for carbon buildup – use speedometer cable and throttle body cleaner to remove carbon buildup
  10. Place intake manifold back in and reconnect hoses, throttle body, etc.
  11. 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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21 Comments

  1. 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

    1. 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

      1. 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?

        1. 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

          1. 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.

        2. 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.

    2. the buildup is prob under your intake mine was

  2. 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

  3. 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 🙂

  4. 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.

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

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

  6. 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.

  7. I have a 1996 Chevrolet Lumina and the EGR code light came on when I scanned using my fixed sensor. Can I just put some fuel injector cleaner and then clear my “ check engine soon” light. I saw in one of the comments that someone Pd. $820.00 to change EGR. My car is not even with that much. What would it cost to have someone look at it and what would be a fair price to have it fixed s I’m a female who knows nothing about checking it myself.

  8. Having the code P0401, does this mean I need a new engine? It also loses all the water or coolant I put in. The truck leaves a line of fluid on the ground.

    1. Sounds like you cracked your radiator and need to replace it to keep coolant in it, which could mean you’re having over heating and smoking which causes build up along with severe other problems and can completely destroy your car I would take it in and have a technician look it over have you been in an accident lately

      1. And that code means the egr valve isn’t functioning correctly for what could be numerous reasons definitely not that you need a new engine but if you don’t get your radiator fixed you could throw a rod or blow a head gasket and just incase you are unaware you should also never open the coolant cap when engine is hot that could cause injury to you and/or crack the radiator

  9. I have P0401 on my o4 kia amanti very annoying i cleaned intake replace egr valve. Egr vacuum solenoid. Hoses cleaned egr tube soaked in gas overnight cannot get rid of code i tryed everything utube told me

    1. My sisters Mitsubshi Galant has this code following having PO403 code. Of which we brought it to our mechanic of which we highly trust for. When we called about the car he said they cleaned it. Well, the light came back so he had use bring it back to replace the EGR valve and only charging for the part. Light came back with same po403 code and being it’s only himself and another mechanic at an individually owned small shop, it’s hard to get in and he needs the car overnight alot etc. So being that the car needed exhaust work we took it to mavis and while there thought we have them check out and they said it was the EGR valve and sensor till I explained the valve was done then they said we would just do the sensor then so we did it and although that code went away it now has this code PO401 only difference being it is flowing/working somewhat now but still not as should be, now the car also has PO421 code and PO456 code. I can’t get an honest answer to the evap code cause our mechanic doesn’t have a smoke machine and when taken to another individual shop she said I don’t need to test it I can see it’s coming from the evap pipe and I can’t help u cause the part was discontinued so I asked scotty kilmer his take and he said fix it with fiber material it’s a low pressurized but despite my attempts to have a shop wrap it with fiber wrap they just want to smoke test the car for the leak themselves and when I had meineke do it they said tjey spotted a leak in the evap pipe clogged it up the best they could anl smoke was too coming from above the tank. So it drew a red flag being the code is very small leak and two separate leaks isn’t gonna equal very small leak, whereas yes a big leak can cover up an small one but this is the other way around! We were told that the underneath of the car is starting to be taken over by rust but yet midas said it honestly isn’t that bad but again they wanna do repair to it so they would say that! We just feel that the EGR system related codes coming up no matter what been done they may never go away reguardless so it may be time to move on with getting another car but that’s no easier lol I am thinking there is carbon buildup somewhere along the line of things that isn’t accessible with out removal of alot of stuff and with labor being the killer in repair the car is beyond worth it! I did try some catalytic converter clearer maybe that will clear it up doubtful but cant hurt to try.

  10. EGR valve was replaced today. Why does it say the problem still exist?

  11. Some people say the problem (car diagnostic code p0401) is the dpfe (differential pressure feedback electronic) sensor and not the egr valve. That is a pressure sensor that checks the differential pressure and it is right on the engine. Costs less than $100 usually and installs with a couple bolts and two hoses go into it.

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