P0404 Code – What Does It Mean & How To Fix It

Causes

The most common causes that would trigger a P0404 to populate on your OBD-II scanner would be:

• The EGR valve is out of its set position when the EGR was commanded to be closed. The ECM monitors the position of the EGR. It has a sensor mounted on top of the EGR valves. If it registers an issue with that valve, it will trigger the code to populate.
• The valve movement of the EGR should be smooth. There should be no jerking whatsoever. If so, the vehicle’s ECM should set the code.
• This can also be caused if the EGR sensor went above the upper threshold at the time the EGM directed the EGR to open.

Symptoms

There are several common symptoms that you should be on the lookout for should you run into trouble code P0404:

• As with many other trouble codes, the check engine light should be illuminated, at which time the code will set in the ECM’s memory.
• You may notice that the engine may have pre-ignition on acceleration.
• This issue with the EGR system can typically cause the engine to run rough. It can even stall or hesitate if it is unable to indicate the proper EGR valve position to the ECM.

Diagnosis

Thankfully, there is a methodical process that you can follow to make sure that you properly diagnose and fix the code. If you stick to these steps in order, you should be able to avoid the common mistakes that can be involved in the fixing of this code

• Make sure that you capture or document the freeze frame data that comes up on your OBD-II scanner.
• Next, clear all of the engine codes off of the scanner.
• Road test the vehicle and retest your car with the OBD-II scanner to verify that trouble code P0404 returns to the screen.
• Next, monitor the EGR sensor PID on the scanner. See if the sensor shows if the valve is stuck open or if it is not moving smoothly enough.
• You will then need to remove the EGR sensor and manually operate the sensor, in order to isolate it to see if the code could be caused by a sensor or valve failure.
• Remove and check the EGR valve to confirm that carbon is not covering it or backing it up. This can cause bad sensor readings.

If you follow through this process methodically, this will limit the possibility of making a mistake during diagnosis. It can also potentially prevent you from repairing or replacing pieces of the vehicle that are functioning properly.

Common mistakes

However, there are some common mistakes that can be made when diagnosing and fixing a P0404 trouble code. These mistakes can include:

• Forgetting to or failing to operate the EGR position sensor manually. This will make it unclear as to whether the sensor or valve has failed, and can lead to replacing functioning components.
• Also, not checking the wiring connection and harness to the EGR position sensor. You should check for problems before you decide to replace the EGR valve or position sensor.

How serious is this?

If an EGR system triggers this code, this may cause the ECM to disable the EGR system, which would then render it inoperative. If the check engine light remains on, this will cause the vehicle to fail emission testing. Know that the EGR position is absolutely critical for the ECM to control the EGR valve the way it needs to so that it can open and close properly.

What repairs can fix the code?

You can fix this trouble code by replacing the EGR valve if it is stuck partly open, due to the carbon buildup in the pintle area. You should do this if the part cannot be cleaned. You can also replace the EGR position sensor. If you have determined this sensor cannot provide the correct input reading to the ECM when it is moved manually during the diagnosis process. You can also fix this problem by repairing any shorted or open wiring to the EGR position connector or sensor.

Related codes

None listed.

Conclusion

This is a serious trouble code that should be fixed as soon as possible, as it can render your vehicle inoperable in some cases. Make sure you follow the diagnosis steps carefully when addressing this problem.