BMW Luxury Touring Community banner
1 - 3 of 3 Posts

·
Registered
Joined
·
876 Posts
Discussion Starter · #1 ·
I'm currently checking out a brake system fault on an '03. Details - when the ignition is turned to on the outer left red light "Brake Failure" starts flashing immediately at 4 Hz. Red brake system light beside it glows steady red. The instant either brake pedal/lever is touched, a servo starts to run and does not stop till the key is turned off. Moving off makes no difference, the system continues to behave the same. Rear brake feels to (still) have power assistance, front brake does not. The fluid has not been flushed in this bike for at least 5 years. I would do a system flush if I thought it would nelp, though it will be a problem if the servo will not stop running. As an aside, this bike has also had an incorrectly sized rear tyre fitted. It currently has a Dunlop Sportmax radial 170/60 17 which is of course not reinforced, whereas the correct size is 160/70 17. The different profile and aspect ratio calculates to 10 mm difference in tyre height (radius), so 20 mm on the diameter, which is approximately 62 mm less per wheel rev than standard. Technically, does anyone know what the ABS system can tolerate in respect to differeng wheel sizes, I would think not too much given the 120 sensor positions per ABS ring. All advice gratefully accepted, thanks, Dennis.
 

·
Wrencher Extraordinaire
2005 K1200LT
Joined
·
15,072 Posts
Don't really know on the tire difference but I would go ahead and flush the unit any way then go from there. But it does not look good. There is really not a lot inside that can go wrong. Just four pressure transducers and the pumps them selves plus the "Brain". the ABS action is done with large electromagnets that control the flow of fluid.

Sounds like one of the transducers is out. The light pattern is indicative on one circuit in the failure mode. If there was just one flashing at 4Hz I would suspect a stuck brake light switch, but you also have a steady light next to it.

Never know there may just be some crud in there and a flush will clear it out. But don't hold your breath.
 

·
Registered
Joined
·
876 Posts
Discussion Starter · #3 ·
Thanks John, yes, I'm afraid I have concluded the same, all is not well with this braking system. I originally thought the front brake switch was stuck on (closed) causing the system to stay in test mode, but this is not the case, the switch works fine. The owner is going to be shelling out around $2500 I feel. I'll still do a fluid flush as fresh fluid needs to be there for the new brake control module. Thanks for the interest, Dennis.
 
1 - 3 of 3 Posts
Top