Very often I come across people who have the ASC or DSC ABS lights/brake on and sometimes with the gas gauge niddle going up and down and speed niddle staying put.
Often as well as all those scary symtoms the mileage does not move either. It is not counted anymore.
Christmas tree time like some like to say
Here is a typical picture of what you might have. For the record, it is a pretty common fault on BMWs
If your car is unable to show the speed and the mileage is not moving anymore, most likely it is due to a faulty speed sensor. I have seen people taking a guess and changing all of them (Extremelly useless). I have also seen people sending their ASC/DSC control unit to some refurbishement company (There is a few who do a good job) or even buying a new module from the dealer just by taking a guess without running a computer diagnostic on their car first.
Many of them are reporting the problem is persistent because they have not done the right thing and replaced the good part.
Remember guys, advices from forums are fair enough to get some directions sometimes, but nothing is ever going to replace a proper diagnostic. And this is the only proper reflex you should always observe first. Stop buying parts for the sake of it if you do not know what is the problem is exactly.
If something like this is happening to you, here is what you must do to avoid buying irrelevant parts.
1. Get your car properly diagnosed (Yes that means no Carsoft, Made in China eBay crap for 65 quids etc…) with a BMW aware computer. A general OBD scanner will not do the job either. So that means Autozone will not work either.
Pay your dealer if need be, or consult your indy, as long as they provide you with a report from a proper diagnostic system (BMW GT1 or independant system such as Autologic).
Make sure they provide you with the report so you can make sure they are not trying to screw you.
Those systems cost well over 1000 quids, so usually specialised mechanics or dealers have these only.
The report will show exactly what is wrong with your car. My bet it is either a speed sensor or a ASC/DSC unit. If it is a speed sensor, it will also tell you which one from the 4 is not responding exactly.
My little finger is also telling me the speedometer data is actually pulled out from only one or two speed sensors out of the 4. But I cannot find an accurate technical source to back this up. If anyone knows, I am glad to be corrected…
Anyway bear in mind older BMW such as E36, E34 etc do not have 4 speed sensors. The speed sensor was on the differential as opposed to newer models where there is 1 speed sensor on each wheel such as e46 etc.
2. If the problem is down to a speed sensor, make sure you inspect it first. It might be disconnected, corroded, dirty. Give a clean before you change it. If the problem persists, just replace it.
3. Now of course if the diagnostic pointed out your ASC/DSC/ABS unit is faulty it should be fixed too.
BMW does not fix this unit, they can only provide you with a new one. They are not cheap usually (Over 700 USD).
Alternatively you can send your faulty unit to a specialist to get it repaired or buy a refurbished one. Either way it will need to be encoded by the dealer or independant specialist.
4. It might also be the case that your steering angle sensor is faulty. If a change is needed, bear in mind it should be encoded and calibrated by the dealer or independant specialist.
You can drive without a ASC or DSC/ABS unit.
Just bear in mind none of those function will be available to you.
So for safety reasons only drive your car slowly for short distances and under ideal weather conditions if you need to bring your car over a garage for example.