Tech Feature: BMW Diagnosing Electronic Accessories – UnderhoodService

Tech Feature: BMW Diagnosing Electronic Accessories

BMW has some of the most technologically

If you’ve read any of my previous articles, you know that I am an old timer and prefer simple cars over today’s high-tech machines. That said, I have owned my share of well-equipped and optioned cars. Even my E30 BMWs were state-of-the art, luxury sports cars in their day.

Power accessories really aren’t options any more with most new cars produced over the last 20 years and almost all European import models. It is ­increasingly hard to find models in the U.S. that do not have power windows, power door locks, alarm systems or even a power sunroof as standard equipment. It is just simply easier for the manufacturers to ship completely optioned cars and the profit margins go up accordingly.

Though I haven’t been to Europe yet, I understand that plain-Jane models are still available and are the norm for most people there. Given that many cars in Europe are owner maintained, that would make sense. More is not always better when it comes to electronics on automobiles.

BMW has some of the most technologically ­advanced and up-to-date cars on the road today. Each year, they seem to advance one system or ­another before the other manufacturers play catch up. Though they may have pushed some features a little too vigorously (like iDrive), for the most part the features on its cars are reliable and trouble-free for years. But, like all things automotive, after a number of years, cycles and abusive treatment, any part can break or at least stop working.

This article will be mainly about what you need to do when a BMW of 10 years or so comes into the shop with a window stuck open, or locked with a dead battery or just a complaint that the systems aren’t working like they did before. This article is not meant to be a repair manual, covering every model, problem or repair. My purpose is to get you to plan a ­diagnostic strategy, working from what you know, and where to look once you have an idea of what has happened.

Whether you are looking at a power window, door or alarm system problem, the first order of business is going to be at the front desk, with questions. There are just far too many variables to start a ­diagnosis without knowing what might have caused a fault.

Important questions that should always be asked of the customer are:

1. Has the battery gone dead or been replaced?

2. Are there any other BMWs in the family?

3. If yes, how many keys are used to operate the car? These may all sound like simple questions, but they can often start the diagnosis, and have a profound effect on how the diagnosis proceeds.

Obvious signs of accident damage, bodywork, ­removed interior panels, or modifications such as ­aftermarket stereo installations, should always be taken into account when planning a diagnosis. BMW, like a lot of other manufacturers, has issued many warnings about the installation of aftermarket electronics and their possible effect on the designed operation of some systems.

Operator errors are also common. This becomes ­especially true when a second owner acquires a car and either doesn’t have or doesn’t read the owner’s manual, and didn’t get the instructions from the dealer at delivery. This can’t be overlooked as a potential problem; just look at the owner’s manual and you can see that there are a lot of functions that can be set, changed, modified or deleted by simple actions. Sometimes, changes are made automatically by the car’s own computer, based on the operation of the systems, or even weather conditions. These conditions are covered in some detail in the owner’s manual, but not so well in the repair ­information that I could source.

One problem we have run into a number of times is the multi-BMW family and numerous keys, not all for the same car. The wrong key can cause all sorts of problems.

The use, or attempted use, of an incorrect key can start a chain of events that may require some reprogramming, parts replacement or dealer recoding if specific faults are present.

The car I based this article on, a 2000 BMW 328i coupe, originally came with four keys. Two master keys that can start the car, unlock the doors, trunk and gas flap. A small, temporary-use key that can start the engine and unlock the doors, and a “valet” key that will work only the doors and ignition. The keys all can energize the EWS (drive authorization). Since the key code changes each time the car is started, it is important to not involve an incorrect key that can cause synchronization problems between the Digital Motor Electronics (DME/Motronic Engine Control) and EWS systems.

Another common problem points to something that happens mysteriously. In looking at pattern failures for a number of systems, there are common cases of “missing” fuses, to go along with multiple blown fuses that can really spoil your day when you are trying to track down a loss-of-power situation. Checking the fuses should always be a first step with electronic diagnosis when a component is inoperative. Of course, a blown fuse is often just the final result of another problem.

Other common situations are those that might seem like multiple system failures, but really are just one fault spread through the interconnection between systems. On most BMW models, all of the accessories like windows, locks, wipers, interior lights and the sunroof are controlled by a single module, the KGM or GM (General Module). The location of this module can be in a number of places depending on the model. In this case, it is mounted on a relay holder above the fuse panel in the glove box. You will need to consult a model-specific repair source to find it on other models.

So you have a car come in with a window that either doesn’t operate, fails to close all the way or doesn’t work like it used to. 
tracing electrical faults is becoming more difficult all the time. having up-to-date and complete wiring diagrams is the key.
1. You need to ask the above questions (see top left column).

2. If multiple keys exist for the same car, you should have all of them before any work is done, to verify that the fault is not in the key.
don't overlook possible faults like this rodent damage when faults are out of the ordinary or 
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