Why you should check your error codes

Many modern cars are equipped with an OBD port that makes it possible to read the error codes logged by the on-board computer. The purpose of this article is to demonstrate why you should learn how to read these error codes.

What are error codes?

Fig 1: Position of OBD port in BMW E90

Many modern cars are equipped with an on-board computer which monitors the engine and the various other systems in the car. Garages and car dealerships use this information to diagnose problems with your car when you bring it in for servicing.  However, it is possible to read these codes yourself by plugging a cable into the OBD port of your car. Figure 1 shows the position of the OBD port in a BMW E90. In the E87 1 series, it is in about the same position.

Why should I check my own error codes?

Some error codes indicate critical problems that might lead to damage to the car or significant lose of performance. When these errors occur, a warning light will be displayed in the instrument cluster, so you will know that there is a problem. However, typically, all you will see is the "check engine" light. This gives you no information about exactly what the problem is or much of an indication as to exactly how serious or urgent it is. If you see this light while driving, you will probably feel under a lot of pressure to take the car into the nearest garage or dealership as soon as possible. You won't be well informed and will have to follow the advice of the garage. That will be a lot of effort and could be quite expensive even if the problem is actually quite simple. If you are able to read the error codes yourself, you will be in a much better position to do some research in advance. Then, you may be able to resolve the problem yourself and, if not, you will be able to make much more informed decisions if you do take the car in.

Other problems are not serious enough to cause a warning light to be illuminated. If you don't check your error codes, you would never know that there was a problem. In some cases, the issue may not be serious, but nevertheless detrimental to the performance of the car. A good example is a broken NOx sensor, discussed in detail in the article NOx sensor replacement. This problem will lead to an increase in fuel consumption, but is virtually unnoticeable other than via the error codes. Hopefully, it would be picked up during a routine service. However, once you had already car in the garage for a service, it is unlikely that you would have the time to understand the implications of driving with this, rather obscure, sensor broken and so come to an informed decision as to whether or not you should have it replaced.

Another type of issue that can occur is one that initially is neither serious nor urgent, but which could potentially become so if left unchecked. For example, a sulphurized catalytic converter (see article) is easily and cheaply dealt with if discovered early. However, if you were unlucky enough that the problem developed to the stage that a warning light were illuminated, then it would be a much more stressful and, potentially, expensive problem to sort out. Another example is the occasional logging of "oil pressure too low" errors. If you see these and the your oil level is getting towards the minimum, then it's a good hint that you should consider topping up or changing your oil even if the official oil-change service is not yet due. You will probably see these warnings a little while before the warning light appears and promptly changing the oil can only be beneficial for engine wear.

How do I check my error codes?

The article How to check error codes answers this question in detail for owners of BMW 1 series E87 cars (2004-2011). Unfortunately, for obvious commercial reasons, car owners are not encouraged to check there own error codes. The process can, therefore, seem rather daunting. However, all that is really needed is to buy a cheap cable and install some software on a laptop computer. Anyone who is comfortable changing some settings on their computer should be able to manage it.