ABS strange behavior ?!¿¡

Just changed the Front pads on the F8, also both bearings, one was shot.
chain and sprockets as well.
then I am doing a test ride. first the ABS lights up and stays on, riding or not, and no ABS. turned the engine on and off and on and off and always the same.
I call the dealer to have an idea, they told me to clean the sensors, did that, test, same thing.
and disconnect the battery, did that, test, same result...
but then, when riding, I try pressing the ABS button for about 4 seconds and the light goes off, and I do have ABS... did the test a number of times and it always work.
Looks like the system is working reverse, the ABS is switched off at start-up, you need the ABS button to put it on!!

anybody else experienced that behavior and knows the cause and solution?

ABS could be tested with the computer but the BMW exclusive importer in venezuela doesn't have a computer since last year !! great service bmw.

Yes. Mine also did that for a while just before the ABS went crazy in the front. Now if I just pull the brake lever carefully the ABS starts pumping like crazy even though I'm far from slipping.

My dealer did a check and couldn't find anything so I unplugged the connector under the seat since I heard "expensive repair" when the dealer said they didn't find anything and had to investigete further..... This was last spring. My battery has been quite weak the whole season and I'm going to replace that. Maybe that can be a cause??? At least the cars BMW make can start acting strange with weak batteries.

Me to had removed the front wheel just before this happened (tire change). As always I removed the sensor and was really careful about that so I have no damage on that one.

When you figure out how you got it to do that in the first place, let the rest of us know!!!

sounds like a feature!!!

Ryan

It is related to the sensor. The air gap is either too big or there is runout on the toothed wheel. Do not credit the ABS with intelligence, it's a 1980's analogue programme transfered to digital format. It sees the ignition come on (or CAN go live if you are so afflicted), it puts a voltage down each wire to see the earth state change and confirm everything is wired up. It looks for both ABS speed signals going up together. If one suddenly falls off along a known decel curve it assumes braking and fires first the hold modulator then the the release on. It is a feedback loop pure and simple.

The ABS sensor is a induction coil. The toothed wheel induces an AC voltage. This is electronically chopped to square wave and the two added. Where they cross a tooth has gone past and can be counted against a simple fixed rate pulse. If the air gap is too big the voltage induced is too weak so it gives up and puts the light on. If the air gap varies the big signal close up followed by the weak one far away is seen as varying wheel speed. First it modulates and when that has no effect it shuts down and puts the red light on.

The cancel button really does nothing except tell the system to stop bothering you with the light. There is no magic "reset" that will make the electronic gremlins behave, it isn't that clever. (Any dealership that charges for a "reset" is just clearing out the error memory, sweeping the fault under the carpet).

So, take a multimeter and set it on the lowest AC setting. Unplug the sensor, connect the meter and spin the wheel. If you see a steady reading over half a volt at steady speed your problem is elsewhere so start wiring loom checks. If you can find someone with an osciloscope you can see it even better. Don't OBDII readers work? These can do the same thing, so think about buying a hand held or talking to any (prefferably German) car dealership. A dealer who thinks he can deal with these systems without OBD isn't worth the name, they are a showroom.

Sorry if this sounds a bit harsh, I spent twenty years trying to get truck dealers to accept you cannot diagnose an electronic vehicle with a packet of woodbines and an adjustable spanner. I'm afraid I view "dealers" who'll sell you a space rocket and expect to maintain it with stone age tools to be contemptable.

Andy

Going to put new front pads on this weekend myself. What do I need to do to prevent this? Sorry guys for your troubles. Dealers should be able to handle this with ease; yet, they never do.

So check that your new bearings are seated properly and not causing excessive air gap on the sensor side of the wheel.

Mine does that after I've been turning it off all day. It will work in reverse. I have spent a little time trying to figure out the combination. Like holding button down and turning key on at the same time . I thought I had it but but no,....:huh Some other threads talk about this. It is like a super secrete feature only known to the software designer. It would be a cool feature to have because it would be great to have in reverse mode for dirt rides. http://www.advrider.com/forums/showthread.php?t=552509&highlight=switch

I have turned mine off after start up twice in one day and then had it seem to default to off on the 3rd start up.

Key off and removed from the bike each time.

There's one of them programmer's "Easter Eggs" in that ABS system somewhere....
We need some one in Germany to feed a few beers to the ABS system programmer and get him to talk ...

Thanks Andy! That was interesting reading. I will check the sensor and the gap.

Sent from my HTC Desire using Tapatalk

Wow! That ABS is a wonderful thing.



ADVISORY WARNING!
This is a sarcastic post.

In the interests of accuracy:


I was trying to edit some helmet camera video and I came across a spot where I start the bike and then say "I'm sure I didn't turn the ABS off last time, but it was off after I started".

I went back through the video to find it and I did stop the engine, turned the key off, but didn't remove it. It also wasn't off for long.

Every other time that day I removed the key.

Maybe that has a something to do with it? Or the computer hasn't shut down completely over a short on/off cycle?


Curioser and curioser...

It has to be really good as someone stole it off my new bike before I purchased it at the dealer :)

tks 3wheels and snowy.
I couldn't report back because I was busy with a stator failure 600 km from home, but I think the problem do arise because of the air gap. With naked eye I can see that the gap is wider than it was or wider than the rear wheel. So I removed the wheel again, the oil seals and checked the left side bearing. It seems to be well seated, in contact with the locking ring, So what else could it be??? Nothing is adjustable there??

P.s. Edit. The symptoms are lamp flashing at start up, off when start to ride and switches to red when one reaches 20kph.

Yep...I'd prefer that feature too.

I will consult my genuine BMW repair manual DVD.

and by Gee, by Jingo, by bloody Crikey did they make me pay for that little piece of digital technology? $140. Australian. Struth Ruth, that was rude.

So the more value we all get out of it the better.

Closest view I can find in the manual:












See if that helps. I'll upload the rest as soon as the first episode of the new season of NCIS has finished. Wifey is yelling at me.

Thanks Snowy
looking at the pictures I must be able to push the bearing further inside,
I'll have to try that.

It was indeed the LH bearing which was not seated properly.
Thanks Snowy

Outstanding result.

That repair and service DVD might pay for itself yet.

I've found that it is a bit light on in detail in a few areas. But still better than nothing.