P0404 Buick Regal Error Code: Causes and How to Fix

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The P0404 Buick Regal error code means that the performance of the Engine Gas Recirculation sensor or valve is out of parameter or the sensor is out of range. It is a generic OBD-II code that must be fixed and cleared before driving your car any further.

P0404 Buick Regal Error Code

The EGR is important to the operation of your vehicle because it redirects exhaust gas into the cylinders, and if the level is too high, the vehicle will stall. In this guide, we will look at how you can diagnose and fix the error code p0404 in a Buick Regal.

How to Diagnose P0404 Buick Regal Error Code?

You can diagnose the P0404 error code in your Buick Regal model with the OBD-2 scanner. It is a generic code that is found on the OBD-II reader. First, you should plug the scanner into your car through the OBD-2 port.

Diagnosing P0404 Buick Regal Error Code

If you discover the P0404 code, this is the clearest sign that there is a problem with the EGR sensor.

  • Follow the steps below to troubleshoot it:

  1. Clear the code and take the car on a road test to see if the engine light will come back on or remain off.
  2. If it comes back on, then it is not a glitch.
  3. Check if the EGR valve is not moving smoothly or if it is stuck open. You can do so by monitoring the EGR sensor pid on a scanner. If it is moving smoothly, move on to the next step.
  4. Remove the EGR sensor and manually operate it to check for a valve or sensor failure. If it is working effectively, then there is no failure, and you can move to the next step.
  5. Check the EGR valve to see if there is a buildup of carbon that is causing the wrong sensor readings.

It is important to diagnose the code quickly and fix the problem because leaving it on can disable the entire EGR system and leave it to be inoperative. Also, it can affect the ECM, which is meant to control the valve in opening and closing. Plus, leaving your engine warning light for too long will make your car fail the emissions test. The EGR error code is critical to the car’s performance.

How To Avoid Mistakes When Diagnosing the P0404 Code?

There are some mistakes that you should avoid when diagnosing the P0404 code, which is not checking the wiring and connections to the EGR sensor before replacing it or the valve. In some cases, the wiring can be damaged, so replacing the sensor or valve will not make a difference. Check the wiring before the replacement.


Also, you can make the mistake of not manually operating the EGR position sensor. This allows you to isolate a sensor or valve failure before replacing the damaged components. Isolating the valve or sensor allows you to figure out the components that are faulty.

Another mistake is to replace the entire EGR valve or sensor without cleaning the carbon deposits and soot that have built up on it. In most cases, once you clean the valve, it will work effectively, and you will not have to replace it. So, try cleaning it first before replacing it.

How To Solve the P0404 Buick Regal Error Code?

You can solve the P0404 error code on your Buick Regal by checking different parts of the EGR system. From removing carbon buildup to replacing the damaged sensor wires, it’s important to assess the system and replace or repair faulty parts. If nothing works, you need to replace it entirely.

Solving P0404 Buick Regal Error Code

  • Here are some solutions to the P0404 code:

  1. Clean any carbon buildup on the EGR valve. The carbon can prevent the valve from opening and closing properly, leading to the engine warning light.
  2. Next, use a scan tool to close and open the EGR valve, as this would help you check if the sensor or valve is out of position. If it is, go to the next step.
  3. Reposition the EGR sensor. After diagnosing the code and checking the sensor, you will be able to figure out what percentage of the sensor is displaced. Then, reposition it to check if it will work.
  4. Check the EGR sensor wires for any damage or burn-out. If there is, then you should replace the sensor wires. This would refer to the circuit wires that have a five-volt feedback to the circuit board. Test the vehicle’s circuit board to check if the wires are working.
  5. If nothing works, then you should replace the EGR valve. You can purchase a new one or contact a mechanic.

The error code P0404 comes up in the Buick Regal when there is carbon buildup on the EGR valve, as this can prevent the valve from working properly. This is an important engine function, and you should address it quickly and clear the code to prevent any engine damage. Use the steps above to solve the problem or replace the EGR valve outrightly to be on the safe side.

How To Identify the Symptoms and Causes of the P0404 Error Code?

To identify the symptoms and causes of the P0404 error code you should observe. If you notice these symptoms, it is a sign that there is something wrong. The EGR system is meant to lower the nitrogen oxide emissions and cylinder temperatures so there will be different symptoms.

To check whether the EGR valve or sensor is working properly, the feedback system of the valve will work with the Power Control Module or PCM, letting the car know that the valve is closed, open, or partially closed. If you notice the P0404 code, it shows that the PCM got data that the valve is working outside of the right parameters.

The PCM monitors the state of the EGR valve to see whether it is completely closed, partially closed, or fully open. Any damage will stop the EGR from operating properly. Aside from this, there are other causes that can cause the code to appear, like the carbon buildup on the valve or the wiring dying out, or getting damaged.

In some cases, the process for fixing and clearing the error code is specific to your car and engine. If you are unsure of how to fix the error P0404 code, you should visit a repair shop instead. The cost will also depend on the type of engine and the vehicle model, and the location of the repair shop. It is important to check the methods in the guide before hiring a mechanic.

  • Symptoms of the Error Code

The main symptom of the P0404 code is the engine warning light. The check engine light will light up on your car’s dashboard, and this happens when the valve or sensor is out of place by fifteen percent or more.

Symptoms of P0404 Error Code

This usually occurs when a vehicle’s engine is working electronically rather than with a vacuum system. You can run a diagnostic to see how much of the sensor or valve is off. Another symptom of the error code is if you notice pre-ignition on the acceleration. Also, the engine might stall, hesitate or run roughly. Your car will be unable to idle.

  • Causes of the Error Code

The main cause of the P0404 error code is if the EGR sensor is moved out of its position. If there is a buildup of carbon around the valve or it is worn out from use for a long time, then the valve can move out of place.

Causes of P0404 Error Code
Another cause is if the EGR valve is moving oddly when it is opening and closing. The valve is meant to be smooth in its operation, and if not, it can trigger the code. Furthermore, the EGR sensor can go above its gas emission limits and trigger the code.

A cause of the error code is shorted or damaged wires that are connected to the EGR valve. This cause only works when there is an electronic system running the EGR valve of your car rather than a vacuum system. Any of these could cause the code to light up.

Frequently Asked Questions

– Can You Drive Your Buick Regal with the P0404 Engine Code?

Yes, you can drive your Buick Regal with the P0404 engine code, but it is not recommended. It is not ideal to drive your car for an extended period of time because the code can cause internal engine damage. It is important to get it fixed quickly before any long-term damage.

– Where Can You Find the EGR Valve in Your Engine?

You can find the EGR valve in the car’s engine, usually located between the intake and exhaust manifold. It is a vital emission control device that sends back the hot exhaust gas into the intake manifold from the engine. Look at your car’s manual to find it.

– What Kind of Damage Can a Faulty EGR Cause?

A faulty EGR can cause damage like problems with the flow and operation of your system. This can lead to performance issues like reduced acceleration, reduction in power, and decreased fuel efficiency. It can also lead to increased vehicle emissions, so you can fail your emissions test.

– Is It Possible to Repair EGR Valve?

Yes, it is possible to repair the EGR valve, but only by cleaning it. This process of cleaning the valve will act as a repair. But, if you thoroughly clean the valve but it still does not work, then it is best to replace it outrightly.

– What Can Block the EGR System?

Soot and carbon deposits can block the EGR system of your car. When the soot and carbon deposits build up around the valve or sensor, it will not be able to close fully. So, there’ll be a flow of exhaust gas into the cylinders even when it is not needed.


If you notice the P0404 Buick Regal error code, you should follow the troubleshooting process to clear it or replace the EGR valve or sensor completely.

Here is a summary of our guide:

  • The P0404 error code in the Buick Regal means that the Engine Gas Recirculation sensor or valve is out of range or not performing properly.
  • You can solve the P0404 error code by cleaning any buildup of carbon, repositioning the EGR sensor, replacing damaged wires connected to the sensor, or installing a new EGR.
  • Symptoms of the P0404 code include the engine warning light being on, pre-ignition on the acceleration, or being unable to idle your car.
  • Causes of the P0404 code include the buildup of carbon on the valve, the valve moving oddly, and shorted or damaged wires that connect to the EGR.
  • When diagnosing the P0404 code, you should check the wiring and figure out what the damaged components are before replacing the EGR sensor.

With this guide, you have what you need to figure out the cause of the P04040 code in the Buick Regal and solve the problem. It is important to troubleshoot your EGR sensor and valve to fix it or visit a professional mechanic instead.

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