ABS Sensor Failure

[apm]

I have had the unfortunate experience of "Brake Failure" whilst approaching a tight corner on my favourite stretch of road! When I went to apply the brakes, all I got was a brake lever that went ROCK hard, and all the pressure that I could muster did nothing to slow the bike down. After running wide through the corner, across the other side of the road and almost collecting the roadside barrier (we call them armco's here in Australia)I gradually slowed down and pulled over to check out what the problem could be. I couldn't see anything obvious other than the Brake Failure message flashing in red and the Orange Triangle Alert light ablaze. Steady as she goes, I took the bike to my BMW dealer who advised that my ABS Sensor failed so all I had left was "residual braking". I can tell you from experience that "residual Braking" is next to totally useless when you need to slow down. It has been repaired but now I feel less than confident in the brakes. Has anyone else had this problem??

Tony.

[JohnBeaven]

If your brake lever went rock hard that doesn't sound like residual braking.

I have tested the residual braking and found the lever travel to increase substantially with sufficient braking power available.

What was the cause of the ABS sensor failure?

[James Clark]

That sounds more like the system dumped full power to the ABS servo. (The servo doesn't apply the brakes, it counters the riders inputs.)

 

 

Maybe it's a new policy to kill all the witnesses to ABS failure?

[apm]

The dealer didn't say why the ABS Sensor failed, they just said that the diagnostics confirmed that the failure occurred and so they replaced it with a new sensor.

[TomfromMD]

That sounds more like the system dumped full power to the ABS servo. (The servo doesn't apply the brakes, it counters the riders inputs.)

Maybe it's a new policy to kill all the witnesses to ABS failure?

Tends to give "Limp Home Mode" a whole new meaning!

Tom

[Pictou]

This has been my experience with residual braking as well. If it went rock hard as described that sounds like a different sort of issue (and one that I have not heard of before).

 

If your brake lever went rock hard that doesn't sound like residual braking.

I have tested the residual braking and found the lever travel to increase substantially with sufficient braking power available.

What was the cause of the ABS sensor failure?

[MadDuck]

My brake sensor failure gave me about 3/8" of lever travel and then no more, ie rock hard. there was no residual braking at all from the lever. The rear brake did however work quite well. The people that say you will always have "residual braking" are wrong. when that computer decides that you don't need to brake you don't get to brake. I believe that the "servo" systems have a "limp home" mode that is undocumented as I never lost both systems and I had sensors fail from bad connectors on each end at different times. If front fails I think you should always have rear and vice versa.

 

I never felt comfortable on the motorcycle again and I moved on to a non abs Harley. Its new owner is quite happy with it and has many miles on it now. It never failed on me after I started applying the rear brake first then the front. Mine was an 05 1200RT. Arguably the finest motorcyle I've ever owned, also the last BMW I am likey to own.

[apm]

Thank you MadDuck.

Finally, someone that knows what I experienced. My bike is also a 2005 R1200RT. What you described with the front brake lever is exactly what happened to me - absolutely NO residual braking, just a break lever that goes rock hard.

Thanks again, sounds like I need to change bikes too. I no longer feel confident in those brakes.

[beemerfan]

There have been a few other posts related to this subject. Unfortunately, the scary stories seem to always involve '05 RT's (like mine). It has me thinking that my first reaction to a braking issue should be to hit the kill switch, then hit the brakes. If the system reacted in some of the ways described in this thread, would it release if it lost power?

[Mudman]

Just hitting the kill switch will not disconnect power to the ABS system. So if you need to restart the ABS you must turn off the key switch.

[Mudman]

While this type failure you describe is rare, it theoretically could occur with a simultaneous failure of two sensors.

 

If the brake switch in the front lever housing failed to go closed as is normal for the switch after releasing of the lever and after it remained open (plausible light braking detected) the front wheel speed sensor stopped working correctly(plausible slowing or stopping of the wheel relative to the rear) it is possible the system would react as you described. The system would read this as applied front brakes with the front wheel sliding. This would enable ABS invention preventing you from applying additional brake pressure with the rock hard brake feel you describe until the wheel speeds were matched. The rear brake would still work normally.

 

Just a front wheel sensor fault (non plausible value for no brake applied) would set a warning light and disable ABS intervention. If the front lever switch is open during the start up the warning lights would not go out until they see a closed circuit and the boosted pressure would not be operable, thus you would be in residual brake mode.

 

If you are following this you should have the front brake switch checked in addition to the front wheel speed sensor replacement. If it is slow or sluggish to turn off the brake light after applying light repeated brakes it should be replaced. It is not reliable.

 

FYI the pump pressure amplifier does not reduce applied brakes, just the opposite. Magnetic force is applied against the control piston to retard apply pressure if the system judges the need to counter wheel lock-up.

Residual brakes from a failure or power interruption will disable the power booster, linked brakes, and ABS intervention. You now have a master cylinder to transfer cylinder to brake caliper hydraulic path with no electronic intervention.

[Agent86]

That sounds more like the system dumped full power to the ABS servo. (The servo doesn't apply the brakes, it counters the riders inputs.)

Maybe it's a new policy to kill all the witnesses to ABS failure?

Tends to give "Limp Home Mode" a whole new meaning!

Tom

If the lever is rock hard, you can't go home limp.

[Rich06FJR1300]

yes, i had the same issue happen to me on my 2002 RT. Turns out the modulator failed and it was 2k to fix! Found a new one on ebay, bought it and the dealer installed it...then i promptly sold the bike and never looked back. The brakes are great, but that servo is just way too much money and for them to only have residual brakes when it fails? ugh! the older models at least you had decent brakes if that happens..now its like you're lucky to be alive if that happens. I did also hear of a lawsuit involving these brakes (some cop on an RT hit a car due to the brakes failing). Seems like BMW was the first to introduce abs into bikes, but they can't seem to get it right for some reason.

[apm]

Thanks Mudman.

I'll also get the brake lever switch checked. The dealer did say that they upgraded the software when they changed the sensor. Don't know if that helps fix the problem.

[apm]

Any article/s on the lawsuit?

 

It would be interesting to see the outcome.

 

[John Bentall]

yes, i had the same issue happen to me on my 2002 RT. Turns out the modulator failed and it was 2k to fix! Found a new one on ebay, bought it and the dealer installed it...then i promptly sold the bike and never looked back. The brakes are great, but that servo is just way too much money and for them to only have residual brakes when it fails? ugh! the older models at least you had decent brakes if that happens..now its like you're lucky to be alive if that happens. I did also hear of a lawsuit involving these brakes (some cop on an RT hit a car due to the brakes failing). Seems like BMW was the first to introduce abs into bikes, but they can't seem to get it right for some reason.

 

I had a ABS modulator failure, picked a used one up from a dealer/boneyard, but continued to ride the bike for another 18 months without any problems. I was pi**ed off at the time though.

Can anyone tell me why we continue to blame BMW design staff for the failure and/or design shortcomings of the Bosch ABS systems, Brembo brakes and Getrag gearboxes delivered to the assembly lines? Is it BMW or the component suppliers who can't get it right