OBD-II codes make it easier to find out what’s wrong with your car—but there are over a thousand codes, which makes it impossible to memorize their meanings and workarounds. Without knowing what the code stands for, fixing the problem becomes a lot more difficult and tedious.
If you’re getting a P0404 code on your scan tool, here’s a quick but detailed guide on what it means, what causes it, and how it can be fixed.
What Does the P0404 Code Mean?
Diagnostic Trouble Code (DTC) P0404 stands for Exhaust Gas Recirculation Circuit Range/Performance Problem. It is a generic OBD trouble code that activates if the powertrain control module (PCM) detects erratic Exhaust Gas Recirculation (EGR) valve performance.
It could mean that your EGR valve isn’t doing what it’s supposed to do in specified parameters such as being fully open when it should only be partially open. This can be bad as, for example, too much exhaust gas can make it difficult for the engine to idle.
The EGR system redirects exhaust gas back into the engine to lower the temperature in the cylinder and lessen nitrogen oxide (NOx) emissions. This system uses a valve to regulate the flow of exhaust coming back into the engine.
The valve is monitored by the PCM, and sends information on whether it’s open, closed, or partially closed.
What are the Possible Causes of the P0404 Code?
Code P0404 usually indicates that there is a carbon build-up somewhere in the lines, or on other occasions, a bad EGR valve.
There isn’t really any way to prevent carbon build-up as it can naturally happen over time, but if you are getting this fault prematurely, here are the possible causes as to why:
- A short in the 5V reference circuit
- Open ground circuit
- PCM-controlled voltage circuit short
- Faulty PCM
- Faulty EGR valve
- Malfunctioning EGR sensor
What are the Common Symptoms of the P0404 Code?
It’s possible to find no observable symptoms of a P0404 code aside from a check engine light. However, EGR valves are known to fail due to poor maintenance, which as previously mentioned, results in carbon build-up. This can block the valve and prevent it from opening or closing completely.
If the valve starts to fail, the engine may begin to experience performance issues like:
- Rough idling
- Poor fuel economy
- Increased NOx emissions
Keep in mind that increased NOx emissions may lead to a failed emissions test. The engine is also at risk of higher combustion temperature, which aside from causing bad mileage, can also cause the engine to overheat.
The symptoms mentioned above can be the result of another underlying issue. Like any other OBD-II trouble code, you’ll need to rule out multiple causes before you can actually get to the main problem and determine the proper fix.
How to Diagnose the P0404 Code
Although P0404 is considered a generic code, the specific diagnosis steps may vary depending on the make and model of the vehicle.
To give you an idea about the P0404 code and how to diagnose it, check out these videos:
How to Fix the P0404 Code
If you’ve dealt with other OBD-II codes in the past, you know well enough that there isn’t a universal solution to fix a code. Aside from diagnosing the P0404 properly, you must have above-average knowledge of working on your car to perform necessary repairs.
If you prefer to resolve the problem on your own, you’ll have to conduct additional research. Once you’ve figured out the underlying cause, look for online discussions about the code and note some of the repairs that have worked for other people. Make sure to focus on confirmed P0404 fixes that have worked for DIY-ers with the same vehicle, as a fix that worked for one vehicle may not work for another.
For example, replacing the EGR valve has been shown to work on a 2005 Dodge Ram 1500—but doing the same thing may not produce the same results on a different make and model.
Before attempting any repair work, remember to consult the appropriate factory repair information. Repair manuals, such as those from Chilton, should come in handy. However, an ALLDATA subscription is much better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information.