Technical Description of OBD-II Trouble Code
Exhaust Gas Recirculation “A” Circuit Range/Performance
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The purpose of the EGR (Exhaust Gas Recirculation) system is to redirect exhaust gas back into the cylinders. By displacing oxygen and fuel, the inert exhaust gas lowers cylinder temperatures, resulting in reduced emissions of oxides of nitrogen. Therefore, it is important to carefully regulate the amount of exhaust gas entering the cylinders through the EGR valve to avoid adverse effects on the engine’s performance (excessive EGR can cause the engine to idle improperly).
If you have a P0404 code, it is likely that your vehicle is equipped with an electrically controlled EGR valve instead of a vacuum controlled one. Additionally, the valve usually has a feedback system that informs the PCM (Powertrain Control Module) about its position (open, closed, or somewhere in between). The PCM relies on this information to determine whether the valve is functioning as required. If the PCM expects the valve to be open but the feedback circuit indicates that it is closed, the code will be triggered. Similarly, if the PCM expects the valve to be closed but the feedback signal shows that it is open, the code will be set.
Symptoms
A P0404 DTC may not exhibit any symptoms other than the illumination of the MIL (malfunction indicator lamp) or check engine light. However, EGR systems are prone to carbon buildup in the intake manifold, which can cause the EGR valve to remain open when it should be closed. In such cases, the engine may idle roughly or not at all. If the valve has failed and is not opening, the symptoms would include higher combustion temperatures and consequently, increased Nox emissions. However, these latter symptoms are unlikely to be noticeable to the driver.
Causes
This code usually indicates either carbon buildup or a faulty EGR valve. However, other possible causes include:
Possible Solutions
Related EGR codes: P0400, P0401, P0402, P0403, P0405, P0406, P0407, P0408, P0409
