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P0401 Ford F150 – Symptoms


P0401 Ford F150

P0401 is a common OBDII trouble code that will appear on the Ford F150. It has to do with the emissions system and means:

P0401: EGR → Insufficient flow

A vehicle’s EGR system is responsible for recirculating exhaust gases to reduce vehicle emissions. There are three main parts of the F150’s EGR system. They are the following EGR valve, Differential pressure sensorand the Actuator Solenoid.

The P0401 is a general code, meaning that regardless of the year (1996+ anyway) and model, it will have the same meaning no matter which manufacturer built the vehicle (Ford F150 or not).

Related: P0420 Ford F150

Ford F150 P0401 Symptoms

Most of the time there will be no symptoms when P0401 activates, other than the check engine light itself. In some extreme cases, you may notice a slight ping or knocking.

  • Service engine soon light– P0401 will turn on the service engine soon light.
  • knocking sound– In some cases, there may be a noticeable knocking coming from the vehicle. It will sound almost like a piston knock.

Ford F150 Diagnostic P0401

Causes of P0401: Ford F150

Diagnosing the cause of the P0401 code on the F150 is usually not very complicated. These are the most common causes:

  • Clogged EGR tube– The tube that carries the exhaust gases back to the engine can become clogged over time. It may also bend or twist. This is especially true if you experience P0401 right after doing some work on the engine. Check the tube to see if it is cracked, clogged, or damaged in any way.
  • The EGR valve itself is bad– The EGR valve itself is usually not the place to start. But, they are certainly the cause of P0401 quite frequently.
  • Vacuum problems– The EGR valve depends on engine vacuum to function. Therefore, if you encounter P0401 and other codes, P0401 may be a symptom of larger problems. For example, if the engine is not running well enough to create enough vacuum to operate the EGR valve, then P0401 will often be triggered.
  • Sensor problem– The differential pressure feed sensor – EGR may fail and cause the EGR valve to stop working properly and throw the code.

F150 P0401 Fix

The good news with P0401 is that it rarely costs a lot of money to fix, and it’s usually pretty easy to spot the problem since it’s right above the engine. Most people see P0401 Insufficient EGR Flow, look up the price of an EGR valve, see how cheap it is, and just put a new one in.

That may be a mistake. Because the EGR valve is not always going to be the culprit. Here are some of the most common solutions to help eliminate P0401:

  • Check the EGR tube – It is a good idea to check the tube going to the EGR because it is often the cause of P0401, it is easy to do, quick, and very affordable to replace. If it is cracked, you will have to buy a new one. If it’s clogged, you can get by by cleaning and replacing it.
  • Check the voltage of the DPFE sensor – If you are good with a voltage meter, check it. Here is a good article on how to do it Still works How to test the DPFE sensor.
  • EGR Valve Test- A vacuum gauge will help you determine if the EGR valve itself has gone bad. Here’s an article from Autozone on how to test it with a vacuum gauge.


Checking your EGR system is relatively easy to do. The most difficult aspect is the DPFE sensor. If you’re not sure you can do it, you can always try everything else first. By process of elimination, you can be relatively certain that DPFE is the culprit. If there is anything you want to add about P0401, feel free to add a comment below. Good luck!


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