P0401 Code: Exhaust Gas Recirculation (EGR) Flow Insufficient Detected


Abbreviation of EGR is Exhaust Gas Recirculation and the primary function of the EGR is to reduce the NOx emissions by rerouting the prescribed amount of gas back into the intake valve that is drawn by the cylinders. And if the emission level increases it indicates that your vehicle is triggering with P0401 Code error.

Definition of P0401 error code

P0401 is an OBD-II generic code and it states as Exhaust Gas Recirculation Flow Insufficient Detected.

What is the meaning of the P0401 error code?

Nowadays, a vehicle with an internal combustion engine consists of the exhaust gas recirculation system, known as the EGR system. The EGR limits up the level of emitted Nitrogen oxide into the atmosphere that is produced during the combustion process of gasoline or the diesel engine.


EGR system recirculates the some of the emitted gases that are released during the combustion process and recirculates them into the cylinder for the next combustion process.
If there are some faults in your EGR system, then the gases that are sent back into the cylinders are unable to participate in the next combustion process.
Due to the faults in the EGR system, the recirculation of the exhaust gases is insufficient and the computer sends a message to the scanning system that your vehicle is triggered by a P0401 error code.

Possible causes of the P0401 error code

There are many causes of the vehicle that is diagnosed with the P0401 error code. Some of them are:

  • Faults or defects in the DPFE or differential pressure feedback EGR sensor
  • Clogged EGR tube
  • Faults in the EGR valve
  • Due to lack of vacuum, the problem in the opening of the EGR tube
  • Blockages in EGR tube
  • Tightly closed EGR valve
  • Problems detected in the DPFE sensor and hoses
  • Blockages in the catalytic converter
  • Carrion or carbon layering in the EGR temperature sensor
  • The problem with the engine computer
  • Electrical defaults in the EGR valve control circuit
  • Faulty Vacuum supply in a vacuum-operated EGR valve

Symptoms of P0401 error code

Common symptoms of the vehicles that are triggered with P0401 error code:

  • Check engine light turn ON
  • Additional codes may be present along with the P0401 error code
  • Hesitation in acceleration
  • Fuel economy fails
  • Failed emission test due to the emission of nitrous oxide
  • Engine ignition pings

The severity of the P0401 error code

This error code is considered serious because of these reasons:

  • Failed EGR valve cause excessive ignition, pre-ignition that can result in damages of the piston and valves
  • The check engine light illuminates and that will cause the failure of the emission test from excessive release of the NOx gases.

How to diagnose the P0401 error code?

If your vehicle is diagnosed with the p0401 error code, the best method to find the actual cause of the error code is to take your vehicle to the mechanic.

  • He will scan codes and documents the freeze frame data to verify the actual reason for the problem.
  • Reset the engine, ETC codes, and will take a small road test of the vehicle to verify whether the codes return.
  • If the code returns then visually checks the vacuum hoses, wiring, and connections to the EGR valve and control solenoid along with the EGR temperature sensor.
  • After checking the above components they will move further by disconnecting and checking if the EGR valve is receiving sufficient engine vacuum to the valve when the control solenoid opens on light-to-medium acceleration.
  • The next process will be checking for EGR temperature sensor changes, and the engine to bog down when the EGR system is opened.
  • At last, to check the excessive carbon build-up, they will remove the EGR valve and temperature sensor.

How to fix the P0401 error code?

After the diagnosis of the P0401 error code, the following repairs or replacements are to be done to troubleshoot the P0401 error code.

  • Replace or repair the leaking or clogged EGR valve
  • Replace or repair a broken vacuum line to the EGR valve or control solenoid.
  • Replace or repair an EGR temperature sensor or clean the carbon off of it to repair it if it does not register enough of a temperature change.
  • Clear the blockages by cleaning the carbon and dirt particles from the EGR tubes to the intake manifold.

P0401 error code is triggered when the EGR temperature sensor is unable to notify enough temperature change when the EGR system opens. So, it is advisable to take your vehicle to the mechanics and get proper treatment of your car.

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