Diagnostic DTC: P0400. Failed the EGR valve, how to fix

DTC P0400 usually occurs on engines with mileage over 60-80 thousand km regardless of the make and model of the vehicle and regardless of the engine type – diesel or gasoline. According to the OBDII protocol, Diagnostic Trouble Code (DTC) P0400 indicates a malfunction in the exhaust gas recirculation system. Let’s find out how to reset the error, why the code P0400 is displayed and how to fix the problem right now.

The peculiarity of this failure code is that it cannot be reset by the usual method. That is, if we remove the terminal from the battery and put it back in five minutes, the DTC will not disappear.

The official decoding of the failure code P0400 is the Exhaust Gas Recirculation system malfunction, and the main regulating device in the system is EGR valve. Any of the errors P040x is related to this system:

Consequently, any of the P040x diagnostic codes may indicate that the recirculation system needs to be cleaned.

Now let’s look at the general principles of the recirculation system (EGR) and find out its most problematic areas, which affect the performance of the engine.
The task of the EGR system is quite clear – a part of the exhaust gases is sent back to the engine. This is done in order to reduce the share of harmful nitrogen oxide in the exhaust.

The situation is the same as with the catalytic converter – the exhaust passes through sensor A, then passes through the EGR metering and distribution valve. The valve sends some of the gases back to the engine and passes the rest to the catalytic converter for further control.

Consequently, the system works in quite harmful conditions, at high temperatures and with dirty gases, which cause deposits on the walls of the system, on the sensors and on the EGR valve. This is when we see error P0400 – as soon as one sensor gets fouled, as soon as the valve loses mobility, as soon as the diameter of the exhaust manifold is reduced even slightly due to fouling, the ECU will instantly alert us to a recirculation error.

It is good, if the error code will look P0401 – P0408, then it is more or less clear which element has suffered from soot or carbon deposits. Common DTC, P0400 and P0403, will make us clean almost the whole recirculation system:

Depending on the engine model, the EGR valve may be located at different points, but it must be connected by a tube or duct to the exhaust manifold:

• On the Ford Focus, it is located behind the throttle valve.
• On the Chevrolet Lacetti the valve is just behind the ignition module.
• On the Opel Astra G and H, the EGR valve is located near the left-hand corner of the plastic engine cover (in the direction of travel).
• On the Opel Omega it is located just under the throttle.

In short, if you want, you can find out where the EGR valve is on any engine, gasoline or diesel – the main thing is to find the exhaust manifold and trace where the vacuum tube goes.

Indeed, there is no universal recipe for cleaning the EGR valve. The way of cleaning and the possibility of cleaning depends in principle on the design of the valve. Older engines with Euro 2 and 3 emissions standards are equipped with mechanical vacuum EGR valves. More modern engines with emission standards Euro 4 and higher use electronic recirculation valves with a solenoid system to control the valve flap.

There is a different cleaning algorithm for each valve, and some are simply indestructible and must be replaced. There are and will continue to be solutions for cleaning the EGR system and valves in particular for each specific engine, so it is not our goal today to review all existing engines in one review. It would be of little use. Nevertheless, if the failure code P0400 occurs, it will be clear that the problem is most likely in the valve and it needs to be cleaned or replaced.

However, the structure of the recirculation system itself is common to all engines, so cleaning the system can be done on any engine. A metal rope and a large bottle of penetrating grease or carburetor cleaning fluid (ABRO CC-220), which is preferable, will come in handy.

To clean the EGR system, we will have to remove the throttle, assessing its condition, find the channels and pipes that go to the EGR valve, generously spray the inside of the recirculation system with carbcleaner and with a metal cable gently remove the soot from the system. After these operations, cleaning and flushing the EGR system, DTC P0400 will not bother you anymore.