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Are you having suffering “check engine” lights with the code P0403? Don’t panic, it might be much simpler than you think. If you have no idea how what it means, you’re in the right place!
Today, you’ll learn everything you need to know about the P0403 code: exhaust gas recirculation (EGR) circuit malfunction.
This code is a general onboard diagnostic (OBD) code for vehicles. It indicates that the EGR circuit has malfunctioned or stopped working. This code belongs to a large list of diagnostic codes of close numbers.
OBD codes are called general because they apply to all brands and car models that are newer than 1996. This means that these codes indicate the same issue and they’re usually fixed in the same way.
However, in rare cases, there might be a few differences between various models in terms of how to fix it.
When the engine is working, the fuel burns through an ideal oxidation reaction. This reaction goes like this:
The oxygen from the air (O2) reacts with organic fuel (simplified as CH) to give out carbon dioxide gas (CO2) and Water (H2O).
These gases are expelled through the vehicle’s exhaust. Unfortunately, overheating of the engine make this reaction hard to achieve ideally. This leads to incomplete burning of the fuel.
Also, Factors like temperature, air pressure, and humidity change affect the final result of the reaction.
These changes affect this combustion reaction and make it hard to achieve. As a result, the nitrogen gas (N2) gets oxidized into different nitrogen oxides. These oxides pollute the environment, causing acid rain and respiratory problems.
The EGR’s job is to prevent this from happening. It works by lowering the temperature of the fuel combustion.
It also reintroduces the unburnt fuel into the engine for complete combustion. They achieve this by recirculating non-reactive gases from the exhaust back into the cylinders.
These gases are responsible for lowering the reaction temperature while burning at a much slower rate. This way, only oxygen burns with the car fuel.
The EGR features a valve that redirects these exhaust gases into the cylinders. This valve is controlled by a power control module (PCM). If the EGR works by applying a vacuum, the PCM is responsible for applying that vacuum by opening the EGR solenoid(s).
These solenoids open at a different time and for various durations according to the conditions of the reaction as needed. They’re mounted on the intake manifold and receive 12 volts from PCM when the engine is running.
If the EGR solenoid(s) doesn’t respond to the PCM, it reads out the code P0403 and the “check engine” lights are displayed on the dashboard.
Many factors cause the P0403 code. Here’s a list of these reasons:
Another Troubleshooting Code about Exhaust Gas Recirculation (EGR)
Usually, you’re not likely to notice any symptoms unless except for the “check engine” light. However, in some cases, you might notice some additional symptoms like:
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Here’s a list of the things that should fix this code:
After clearing the code, they take the vehicle on a test drive to ensure that the problem doesn’t return.
With that said, you now have a better understanding of the P0403 code. As you can see, the range of symptoms in this code is vast.
This means that it can be as simple as illuminating “check engine” light all the way to a dying engine that can be a bit serious on the road.
Such a code should give you more than enough time to reach a place where you can check it safely. However, the sooner you fix it, the better!
James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.