Error code P0401 is an exhaust gas re-circulation or EGR. It is also considered as an essential part of vehicle emissions system and, at the same time, it is used to lessen the pressure and combustion temperature to easily control the Nitrogen Oxide. In addition to this, the error code P0401 comes with three parts: the differential pressure sensor, actuator solenoid and EGR valve. These parts work together to deliver an accurate amount of re-circulation based on the load and engine temperature. The error code P0401 simply means that the OBD detected an insufficient amount of EGR.

The error code P0401 is a very common code and there are plenty of solutions that you can use to fix this error. When it comes in solving this type of error, you don’t need to worry about spending a significant amount of money.


The error code P0401 is also known as insufficient EGR flow. It simply means that there are not enough gases flowing back into the incoming air to the engine. EGR stands for exhaust gas re-circulation. In addition to this, the EGR system has three important parts – the actuator solenoid, DPFE and EGR valve. The car manufacturers decide to create the EGR system so that the burned exhaust gas can easily flow back into the engine, especially when the EGR valve is widely open. Aside from this, it can lower the combustion temperatures reducing the emissions. This OBD error code means that the car’s computer has tried to open the EGR valve however it can’t get enough exhaust gas into the engine. Furthermore, the EGR systems are being controlled by engine vacuum with the use of valves and hoses. In the present time, it is being controlled by electrical solenoids.

Common Symptoms

In terms of error code P0401, you can notice issues such as pre-ignition knock, especially when the engine is under load or when a vehicle is at higher speeds. Some of the issues and problems include stalling, rough idle, poor fuel economy, lack of power and surging. Pinging noises or engine knocking are also considered as one of the common symptoms of error code P0401.

Possible Causes

The error code P0401 most likely means that one or more of the following has happened:

  • The DPFE or also known as differential pressure feedback EGR sensor needs to be completely replaced or it is faulty.
  • There is a blockage in the EGR tube
  • The EGR valve is faulty
  • The EGR valve many not be opening due to lack of vacuum.
  • Restricted or clogged EGR passages
  • The EGR valve stuck closed
  • Problems with DPFE sensor and hoses
  • Clogged catalytic converter
  • Carboned up EGR temperature sensor
  • Engine computer issues and problems
  • Electrical problems with EGR valve control circuit
  • Vacuum supply problem at the vacuum operated EGR valve

How to Check

The best way to diagnose error code P0401 is to avoid throwing parts at it. According to some research, error code P0401 is one of the error codes that will come back – especially if not accurately checked.

  • If you are planning to take it to a mechanic, be sure to have the diagnostics done at the dealer since they know the usual problems and issues as well as they have the newest repair information.
  • If your engine computer needs to be completely reprogrammed as a crucial part of the overall repair, your dealer can greatly help you with this.
  • But, if you want to check it yourself, it is very imperative to check for the common problems like damage or bad DPFE sensor.

How to Fix

Car manufacturers have their very own design of EGR system but the two major causes of error code P0401 are the passageways or valve itself that exhaust gasses pass through. Most of the time, the error code P0401 is caused by clogged EGR passages so removing the sensor will greatly help you to access to them. It is also important to check the vacuum hoses and the wiring going to the EGR valve. In fixing error code P0401, here are some of the possible solutions you should take into account:

  • Use vacuum pump to open the EGR valve while monitoring the DPFE voltage and RPM engine.
  • Clean the EGR valve and tubing to remove the deposits
  • Check the voltage at DPFE and compare to specified values, You can also refer to your repair manual for your specific model
  • Replace your DPFE sensor with high quality one
  • Replace the EGR valve