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ABS problem - making sure I have this right

6K views 17 replies 11 participants last post by  540iman 
#1 ·
99 540it sport - I too have abs/dsc/brake issue.

I am dizzy from reading the amazing array of ABS/DSC wheel sensor, etc. issues. I am reading of course because I share the problem of the tri warning lights (triangle, brakes, abs). I just want to make sure I am understanding the basics of this wonderfully erratic system. My mechanic diagnosed (GT-1) right rear abs wheel sensor failure and offered to replace for $285. He has previously replaced the same sensors on two or three other wheels over the past couple years and so I decided I needed to try fixing this one myself. Was excited to get it done after reading how easy it is and seeing how much cheaper the parts can be had direct rather than through my mechanic. Then I got engulfed in the web of info on this site about this problem, and the amazing draft DIY piece by Bluebee on the topic. My understanding is that if my right rear sensor was bad my cruise control would not work. Is that right? Well tried it out tonight and to my dismay, the cruise control seems to be working spot on. Is this an absolute? If the cruise control works than the right rear sensor must be OK? Does this mean then that the most probable culprit is my ABS module?

I am sorry for starting a new thread on this topic, but I just wasn't sure how else to ask. And I definitely felt a huge information overload so just looking to get confirmation and then I will probalby go for an ABS module rebuild (which of course will mean lengthy evaluation of the rebuild alternatives available). Thanks for all your help.
 
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#2 ·
Well, this is pretty tough to determine, in all honesty.

You can replace the sensor, without the anal rape, for around CAD70 and 1/2 hr to 1 hr time if you're moving slow (like me***8212;either too little force or wayyyyyy too much it seems, so I take it slow).

If this doesn't solve the problem, you can have the car diagnosed again or you can have the module sent out. As Bluebee says, most people advocate this as the module is almost guaranteed to go at some point in the car's life. If the problem is still not dealt with even after a replacement module, you'll have to get the codes read; I believe that the better rebuilders thoroughly test the module before sending them back.

HTH.
 
#3 ·
Anyone have a better understanding of the relationship of the various wheel sensors to the various related systems failures? I don't want to needlessly replace sensors if I still have to do the ABS module. Is it possible for right rear sensor to be bad and still have cruise control work?
 
#4 · (Edited)
You probably went over this excellent DIY by bluebee, read post #48 carefully:
http://www.bimmerfest.com/forums/showthread.php?t=356272&highlight=bluebee+abs&page=2

Then read a bit on how Bosch ABS, DSC works. It is not that hard to understand in layman's language.
- The Bosch (or Siemens) computer is the Brain.
- Speed sensors count the number of revolutions on each wheel. Inisde each wheel sensor there is magnetic winding, similar to a transformer.
On the driveshaft (or hub if not the drive wheel) there are splines, or teeth, that the sensors read off.
Whenever the wheel is rotating, the sensor reads the number of teeth counted per second and convert that into a digital square signals (it looks like sine waves but it is square instead of waves) that only the ABS Brain understands and then executes appropriate reaction such as reducing braking effect on the wheel that slips on ice/snow etc.



http://www.bimmerfest.com/forums/showthread.php?t=401930&highlight=rear+sensor+axle

You likely has 4 sensors, the number of sensors depend on the models and year of production.

So the possibilities are:
1. Bad ABS Module
2. Bad wiring from sensors
3. Bad sensors themselves.

My suggestion:

1. If you have a buddy with the similar car, then swap part to see if it solves the problem.
2. Proper diagnosis = proper solution
3. Or trust your mechanic computer and replace the rear sensor as suggested. If it fixes the problem, great.
If not, then the bad news is that you just spent $83 (or more) for a new part that was not your problem, the good news is that the part is likely to fail soon, so the money is not all that wasted anyway and also if future issues show up, the part you just replaced is the LEAST likely to be suspect...:)!

PS: FYI
34-52-1-182-159 ABS Sensor Front Left/Right (2 Per Car) 540i 0i thru 08/98 E39...$111
34-52-1-182-160 ABS Sensor Rear Left/Right (2 Per Car) 540i 0i thru 08/98 E39....$117

34-52-6-756-375 ABS Sensor Front Left/Right (2 Per Car) 540i 0i from 09/98 E39....$66.
34-52-6-756-376 ABS Sensor Rear Left/Right (2 Per Car) 540i 0i from 09/98 E39....$83
 
#5 ·
It most likely is the abs unit, have it rebuilt and be done.
 
#6 ·
+1 If you look, you will see that BlueBee and I collaborated a lot of this subject. Even a GT-1 can be fooled to diagnose a bad Module as a bad sensor. There is NO machine made that can diagnose a bad sensor 100% as the problem can, and often is, the input circuit for that sensor inside the module. The Gt-1 or any other machine can not tell the difference. Only if the module is disconnected from all sensors can you determine 100%. Unless you are handy with a VOM, the just replace the module and be done with it. If you are handy with a VOM, using the diode check feature of the VOM, you can do an incredible job of diagnosing the speed sensors. If I had to do all over again, I would test all four sensors and if all good, change the module. You can also swap rear sensor left to right and vice verse and see if the car acts any different in any way. Speedo, cruise, anything changes. If it does, but one rear speed sensor and try it at both positions. Rears are the same and fronts are the same.

If car acts the same, you can chance a rebuild (BBa or Module masters) or buy a new one from Jared, get it coded, and go from there.
 
#8 ·
Can't definitively answer your question about cruise. However, the percentages say module, not sensor. And as said, you can get a false reading. My indie showed that the problem for me was left front, and it wasn't.

So go ahead and repair module -- it will cost less than the sensor quote! I used BBA-Reman. Here's a post I wrote on it, very easy to do:

http://cparente.wordpress.com/2008/11/12/diy-the-answer-to-abs-problem/
 
#9 ·
Many thanks

Thanks everyone for good thoughts and suggestions on the situation. Sorry so slow on a reply - I wish this site would send me an e-mail when there was a response to my post. No change in the status. I have been too busy to do anything yet. I think I will do the ABS module rebuild - now to pick which one. The ATE (www.autoecu.com) $105 price is hard to resist. I saw a few good references on this company. Anyone have an horror stories to report?
 
#11 ·
Afraid I do not have any friends with same car so not able to try swapping the module. Not sure it would work anyways because it sounds like the module is coded to the particular car it is installed in - I suppose I could try swapping out speed sensors, but the whole problem is so intermittent that I think that approach could be maddening. At this point I am planning to do the module rebuild and probably will try the bargain basement ATE outfit (unless I hear any scary stories about this firm). Thanks,
 
#12 ·
Not sure [a swap] would work ... because it sounds like the module is coded to the particular car it is installed in
Interesting idea of swapping out the ABS modules.

A new module would have to be coded but I wonder what happens if you swap a donor module with the original module just to see if the three lights go out on the instrument cluster ... and then swap 'em back.

The hope is this quick-swap would NOT need any encoding and, I hope, it wouldn't destroy the coding in the donor ABS module.

But who wants to risk the donor module w/o knowing whether or not it will destroy the existing encoding. Does anyone know?

 

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#14 ·
Happy BBA Remanufacturing customer

I sent my ABS module to BBA to be rebuilt. The process took less than 1 week. Cost was $155 (e-bay auction). With the rebuilt abs unit installed all dashboard warning lights have gone out (ABS, Brake, DSC triangle, check engine). The process was very simple. I am a very satisfied BBA customer.
 
#16 ·
had the same prob of tri warning lights after car came back from the garage ,looked under the bonnet and the small two pin plug on the back of the abs unit was loose pluged it back in and haypresto lights went off ,not sure what plug this is but its worth checkin the easy fixes first
 
#17 ·
I tried to clean my drivers side (LHD) sensor and broke it. For the two days I waited for a new one I had the 3 lights on, no fuel consumption reading, no speedo and of course no cruise. That sensor is obviously the speed sensor as well as ABS. I don't think the RH Rear one would affect the cruise.
 
#18 ·
I cannot recommend ATE as a rebuilder of modules. I would rather not go into the details, but I have first hand knowledge. I would trust BBA or module masters except that I feel they are way over-priced. To answer bluebees question, if you swap in a module from another car regardless of the similarity or the year, it will not work without being recoded. The module, for whatever reason only BMW can speak to, must be linked to the car's vin. I would think it was done just to encourage the sale of new modules, but in fairness it could be due to the safety and liability issues of someone installing a similar, but slightly different module coded for a heavier or lighter car. The response of the module must be appropriate for the suspension, weight, and so forth of the vehicle it is in. The only way to change the module to be 100% sure it is matched in terms of gain, dampening, and so forth is to know the vehicles vin#. The module checks the vin coding every time the car is started. You can't get around this. Swap modules left rear to right rear and if you lose or gain any functions ie. speedo, cruise, etc. then you have a bad sensor. No change and you are barking up the wrong tree.
 
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