Skip the auto shop - Our mechanics make house calls

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

Check Engine Light

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Post a question and get free advice from our certified mechanics.

ASK A QUESTION

More related articles

How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
P2159 OBD-II Trouble Code: Vehicle Speed Sensor B Range/Performance
Diagnostic Trouble Code (DTC): P2159 P2159 code definition Vehicle Speed Sensor B Range/Performance Related Trouble Codes: P2158: Vehicle Speed Sensor B P2160: Vehicle Speed Sensor B Circuit Low P2161:...


Related questions

Q: P0030 p0015 chk eng lgt on whining noise stuck 2 gear 1 yr had car let son drive 2 NV havent chk fluid N trans hope it wasnt low

The code P0015 is a bank 1 timing over retarded warning. The P0030 code stands for the heated oxygen sensor malfunction, which also pertains to bank 1. The oxygen sensor malfunction could be due to a failed sensor, heater, or...

Q: Code p0101

The P0101 trouble code may keep returning if the engine computer does not see the MAF sensor input within a specified range when it is testing the MAF input. The input can be wrong if the engine has another problem...

Q: Engine is running rough and P0401, P0171 and P0174 codes.

The first thing to check is to see if the EGR solenoid will release the vacuum when the electrical connector is disconnected. If it still doesn't release the vacuum then the solenoid should be replaced. The codes need to be...