The latest vehicles contain an exhaust gas recirculation (EGR) system to control exhaust gas emissions. Your vehicle’s EGR system contains three major parts: the EGR valve, EGR solenoid, and EGR sensors. The EGR valve regulates the EGR (exhaust gas recirculation) flow. When something goes bad with the EGR valve circuit, your powertrain control module (PCM) triggers the P0404 code. This article explains the P0404 code meaning, causes, symptoms, and fixes.
P0404 Code Definition
The diagnostic trouble code (DTC) P0404 stands for “Exhaust Gas Recirculation Circuit Range/Performance”.
What Does the P0404 Code Mean?
The P0404 code indicates that your powertrain control module (PCM) detects that the performance of the EGR valve or sensor is not within the specified limit.
Exhaust gas recirculation (EGR) is an emission control technology used in modern IC engines (gasoline/petrol engines and diesel engines) to reduce NOx emissions.
The EGR system of your vehicle recirculates a specific amount of the exhaust gases back to the engine to reduce the temperature of the combustion chamber and reduce the emission of nitrogen oxide (NOx).
The EGR system is most commonly used in diesel engines because these engines release very high levels of nitrogen oxides which are injurious to the human body and environment.
This system contains an EGR valve and ERG sensor to control the flow of exhaust gas back to the engine.
The EGR position sensor measures the position of the EGR valve and sends this data to the powertrain control module (PCM). The PCM uses the EGR sensor data to determine whether the valve is open, closed, or partially closed.
When the PCM of your vehicle detects an issue with the EGR flow, it triggers the DTC P0404.
Symptoms of P0404 Code
A vehicle with a P0404 code usually triggers the following symptoms:
- Rough idling
- Check engine light illumination
- Poor fuel economy
- Ringing noise on acceleration
- Possible stalling
- Failed emissions tests
- Difficult to start the vehicle
- An increase in the emissions of exhaust
Causes of P0404 Code
A vehicle usually triggers the P0404 code due to one or more of the following causes:
- Bad EGR valve
- Faulty EGR sensor
- Open ground circuit
- Bad MAP sensor
- Faulty MAF sensor
- Using low-quality fuel
- Short trips
- Carbon buildup in the EGR passages or on the EGR valve
- Damaged wires or loose connections
- Bad Powertrain Control Module
- Intake leak
How to Diagnose the P0404 Code
Follow the following steps to diagnose the P0404 trouble code:
- Use an OBD-II scanner to verify the existence of the P0404 trouble. Utilize the freeze frame data to identify the main issue.
- Inspect the EGR valve for damage.
- Properly inspect the EGR system wires for damage or corrosion.
- Properly inspect the connections to the EGR system.
- Properly examine the EGR valve for carbon buildup. If your valve is clogged, clean it properly.
- Inspect the MAP sensor or MAF sensor. Clean the sensors if they are dirty.
- Properly inspect the EGR passages for a leak or blockage.
- Properly inspect for intake leaks.
- Inspect your PCM for the issue.
- Clear the codes and perform a test drive.
Common P0404 Code Diagnostic Mistakes
- Replacing the unnecessary components
- Not operating the EGR position sensor manually to isolate a valve or sensor failure before replacing the other parts
- Replacing the EGR valve without inspecting the vacuum system for leaks
- Not inspecting the connections and wires to the EGR system before replacing the EGR sensor or EGR valve
- Installing the new EGR sensor or EGR valve without testing it.
How serious is the P0404 Code?
The severity level of the P0404 code is considered moderate. This code indicates an issue with your EGR system. A faulty EGR system may increase the emission of exhausts which are very harmful to the atmosphere. However, the presence of this code may also lead to the failure of the emission test.
What repairs can fix the P0404 Code?
One or more of the following repairs can fix the P0404 code:
- Replacing the faulty EGR valve
- Cleaning the carbon buildup in the EGR temperature sensor
- Replacing the bad EGR pressure sensor
- Cleaning the blocked EGR pipes
- Replacing the damaged catalyst in the exhaust
- Repairing the damaged vacuum lines to the EGR valve
- Fixing the intake leak
- Updating the software of the PCM
P0404 Code Repair Cost
The P0404 code fixing or repairing cost depends on the nature of the repair. To fix this code, you need one of the below-given repairs:
| Parts | Cost |
| EGR valve replacement | $220 to $370 |
| MAF sensor replacement | $180 to $520 |
| EGR pressure sensor replacement | $90 to $130 |
| EGR temperature sensor replacement | $210 to $240 |
| Vacuum leak repair | $90 to $220 |
How to Prevent the P0404 Code?
You need to follow the following control measures to prevent the P0404 code from triggering:
- Regular maintenance of your vehicle
- Clean your intake manifold and EGR valve after every 30,000 to 50,000 miles
- Use high-quality fuel
- Avoid short trips. Short trips usually prevent the engine from reaching up to the normal operating temperature, causing the accumulation of carbon.
- In case of poor engine performance, contact a professional as soon as possible to address the issue
- Drive your vehicle on the highway regularly. It helps to keep the EGR system clean.
FAQ Section
Can I drive with code P0404?
Yes, you can drive with the P0404 code. Driving with this code for an extended period of time may cause internal engine damage. Therefore, you should fix this code as soon as possible.
How to fix an exhaust gas recirculation circuit malfunction?
- Verify the existence of the exhaust gas recirculation circuit malfunction code using an OBD-II scanner, and then reset the fault code
- Replace the damaged or faulty EGR valve
- Replace the open EGR vacuum solenoid
- Replace defective EGR sensor
Can I clean my EGR valve myself?
- Wear acid-resistant gloves to clean the valve. Also, wear safety goggles as carbon deposits can fly away during the process.
- Spray EGR valve cleaner on the carbon deposits.
- Use a drain cleaning brush and blunt scraper to remove carbon buildup.
Can a faulty EGR valve damage engine?
A bad EGR valve may generate different drivability issues. A bad EGR valve generates different performance issues, including poor acceleration, poor fuel economy, a reduction in power, or a failed emission test. It may also cause an increase in the exhaust emissions.