Sulfurized Catalytic Converter

If you are in the habit of checking the error log of your BMW, you might see repeated warning about a sulphurized catalytic converter. In this article, we describe what this means and how to rectify it.

Symptoms

If you regularly check your error codes, you might come across this one.

0x30EA  0x30EA DeNox-Katalystor, verschefelt.
gespeicherte Schwefelmasse im Katalysator    696.32 mg

At present, this is not a critical condition and so no warning lights will be illuminated at this stage to alert the driver to the problem.

Meaning

The car is equipped with a catalytic converter whose job is to breakdown pollutants in the car exhaust. For example, nitrogen oxides are broken down into harmless nitrogen and oxygen; see the article Nox sensor replacement. The catalytic converter performs best when the exhaust gases are hot, such as when driving on the motorway. When the engine is being underutilized, for example if the car is used for many short trips at low speed in town, sulphur can accumulate in the converter; see Air-fuel ratio (Wikipedia). Too much sulphur reduces the effectiveness of the catalytic converter and, therefore, an increase in emissions.

Solution

Fortunately, this is a very easy problem, especially if caught early. As the problem is caused by too many short journeys, the solution is to take the car on the motorway and drive fairly aggressively. For example, I managed to clear the code above by taking the car for a 20 mile run on the motorway, accelerating hard in sports mode (or a low gear, if driving a manual) when I needed to pick up speed and holding the car at 70 mph as much as possible. In contrast, two 11 mile runs partially on motorway and partially on A roads with 40 or 50 mph speed limits, was not enough to clear it.

Regular checking of error codes

This problem is a good example of why it is important to learn how to read your car's diagnostic error codes and to do so frequently. This problem will generate errors codes weeks or months before it triggers a warning light. If you spot it early, there will be less sulphur in the exhaust, so it will be easier to clear. Furthermore, you need not be in a hurry to fix it, so you can wait until you need to make a journey of 20 miles or so and then modify your route to make as much use as possible of motorways or fast A roads, rather than having to make a trip specially. If you don't check your error codes and you're not lucky enough to clear it by chance then you won't know about the problem until you see a warning light. If you do see a warning light, you probably won't know why unless you take the car into a garage or back to the dealer, at which point a problem that could have been resolved for free will probably be expensive to fix and will have caused a lot of unnecessary stress.