P0401 OBD-II Trouble Code: Exhaust Gas Recirculation Flow Malfunction

Our certified mechanics come to you · Get a fair and transparent estimate upfront

Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0401 code

P0401 is a diagnostic trouble code (DTC) for "Exhaust Gas Recirculation Flow Malfunction". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$20.00
Toyota$20.00
BMW$20.00
SCHEDULE P0401 DIAGNOSTIC Get a fair and transparent estimate upfront

P0401 code definition

Exhaust Gas Recirculation Flow Insufficient Detected

What the P0401 code means

P0401 is an OBD-II generic code that the engine control module (ECM) detected the engine exhaust gas recirculation (EGR) valve is not flowing enough recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold.

What causes the P0401 code?

  • The EGR valve is not opening all the way due to a low vacuum opening the valve from the EGR control solenoid or the EGR not being able to hold vacuum.

  • The EGR temperature sensor is not registering enough of a temperature change when the EGR valve is opened.

  • The EGR passages are partly blocked and will not allow enough flow of exhaust gases into the intake manifold.

What are the symptoms of the P0401 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory.
  • The engine could have an engine ignition ping or knock on acceleration.
  • The engine will fail emissions from excessive NOx in the exhaust tests.

How does a mechanic diagnose the P0401 code?

  • Scans codes and documents the freeze frame data in order to verify the problem.

  • Clears the engine and ETC codes and road tests the vehicle to verify whether the codes come back.

  • Visually checks the vacuum hoses, wiring, and connections to the EGR valve and control solenoid along with the EGR temperature sensor.

  • Disconnects and checks the EGR valve is getting enough engine vacuum to the valve when the control solenoid opens on light-to-medium acceleration.

  • Checks for EGR temperature sensor changes and engine to bog down when the EGR is opened.

  • Removes EGR valve and temperature sensor to check for excessive carbon buildup or partial blockage of the EGR tubes from the valve to the intake manifold.

Common mistakes when diagnosing the P0401 code

  • Failing to check and clean the EGR passages when replacing a defective EGR valve.

  • Condemning a good EGR valve when the EGR temperature sensor has excessive carbon buildup on it causing the failure code.

  • Failing to check to see if the EGR control solenoid will hold vacuum before replacing the EGR valve.

How serious is the P0401 code?

  • A failed EGR valve can cause the engine to have excessive ignition pre-ignition that can cause internal engine damage to the piston and valves.

  • The Check Engine Light on will cause the vehicle to fail emission testing from excessive NOx gases.

What repairs can fix the P0401 code?

  • Replacing the leaking or clogged EGR valve

  • Replacing a broken vacuum line to the EGR valve or control solenoid

  • Replacing an EGR temperature sensor or clean the carbon off of it to repair it if it does not register enough of a temperature change

  • Cleaning carbon out of EGR tubes to intake manifold to clear any blockages

Additional comments for consideration regarding the P0401 code

Code P0401 is triggered when the EGR temperature sensor does not see enough of a temperature change when the EGR is commanded to open. These sensors tend to get a lot of carbon buildup that causes them to lose sensitivity to the heat from the EGR gases.

Need help with a P0401 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

trouble codes
P0401
Check Engine Light

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0401 code.

SCHEDULE P0401 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating


YourMechanic Check Engine Light is on Inspection Service

Average Rating

4.8/5

Number of Reviews

5,395

Rating Summary
4,978
202
50
30
135
4,978
202
50
30
135

Anthony

6 years of experience
18 reviews
Anthony
6 years of experience
Jeep Grand Cherokee - Check Engine Light is on - Carmichael, California
Anthony was great! We are very happy that we chose to go with this company instead of the overpriced and slow service we get from the Jeep dealership. He was on time and did the job just as expected. He identified a couple of other things that need to be done before the problems get worse. We appreciate having a technician give us direct feedback regarding our vehicle, rather than a service advisor (salesperson) that we've had to deal with in the past at the dealership. We'll be booking the addtional services very soon and will definitely request Anthony again now that he is familiar with our vehicle!

Michael

37 years of experience
113 reviews
Michael
37 years of experience
Subaru Forester - Check Engine Light is on - Santa Fe Springs, California
Michael was punctual and courteous. He knows what he’s doing and I would absolutely recommend him to anyone.

Anthony

6 years of experience
18 reviews
Anthony
6 years of experience
BMW 740Li - Check Engine Light is on - Roseville, California
Very helpful in finding out the fault codes in my bmw 740 li. It was simple fix and that the two tube hose just had to be connected and my drive train malfunction went away. This saved me from having to go the an expensive dealership. Anthony has a good attitude about his work.

Breck

19 years of experience
613 reviews
Breck
19 years of experience
Ram 1500 - Check Engine Light is on - Houston, Texas
Breck did a great job working on my truck. Showed up on time, found any issues I had on my truck and explained everything to me so that I understood what was going on. Went above and beyond, definitely will book him for future appointments.


Related questions

Whats wrong , engine codes p0605,p0842,p0642, and p0401 thrown twice , light front end damage wothout airbag deployment

Hello, thank you for writing in. If the vehicle was in a wreck, the issues are likely independent from each other. One issue seems to be a powertrain control module electrical malfunction. This could be an issue with an input...

P0421 and P0401 codes have appeared

Hello. The codes P0421 and P0401 refer to the oxygen sensor and EGR valve, respectively. It is possible that an issue with one is causing the fault to be seen by the other, as they will work loosely together. It...

Egr valve insufficient flow

Insufficient EGR flow is probably not the cause of the rough or low idle and thus is just a coincidental fault. You should repair it and perhaps first, just to be absolutely sure, but rough idle is more likely due...

More related articles

P0102 OBD-II Trouble Code: Mass Airflow (MAF) Circuit Low Voltage Input
P0102 Trouble code definition Mass Airflow (MAF) Circuit Low Voltage Input The code P0102 code is often associated with P0100, P0101,...
P0490 OBD-II Trouble Code: Exhaust Gas Recirculation "A" Control Circuit High
P0490 means the PCM has detected an abnormally high voltage within the exhaust gas recirculation system, often due to clogging.
P0019 OBD-II Trouble Codes: Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor B)
P0019 P0019 code definition Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor B) What the P0019 code means P0019 is the OBD-II generic code indicating that the crankshaft and Variable Valve Timing (VVT) position sensor B for bank 2...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com