Battery related ABS faults in BMW motorcyclesBattery Caused ABS faults
If you own an ABS equipped BMW motorcycle, insufficient battery voltage can cause an error in the initial brake systems self-test, temporally disabling your ABS. This article describes how to diagnose this issue and some solutions to remedy it.
ABS Self-Test
ABS equipped BMW motorcycles (including ABS-I, ABS-II and I-ABS models) performs a self-test every time you start your motorcycle and another test after you achieve sufficient speed (about 3 MPH / 5km/h) to perform additional dynamic tests.
Different model motorcycles indicate ABS self-test errors in different ways, but generally speaking, any ABS (also “Brake Failure” on later models) lights that remain on or flash after the bike is in motion, indicate one or more aspects of the test have failed. Any error that occurs at this time will prevent the ABS system from activating and will be indicated (after the motorcycle reaches sufficient speed) by ABS (or similar) lights remaining on, or flashing alternately. It is perfectly normal for the ABS lights to flash in unison before the bike has reached 3 MPH (5 km/h).
The Problem
While there are a number of reasons why the ABS self-test may fail, a very common condition is low battery voltage. Such a fault may be indicated by the two ABS lights remaining on or flashing intermittently of one another after the bike is motion. (Non-battery related ABS faults are also indicated this way).
It has been suggested [include sources] that the batteries supplied by BMW may contribute to this type of fault as they frequently produce lower voltages than many aftermarket, sealed types. This may be particularly true of older and more worn batteries which are less capable of producing adequate voltage to pass the ABS self-test.
Diagnosis and Solutions
If you find your ABS lights are intermittently flashing, or remaining on while the bike is motion, the following tests may help you determine if the battery is the culprit.
1. Try charging your battery – this will sometimes remedy a battery related ABS fault. If the results don’t last, you might consider purchasing a new battery. If your bike is fitted with a flooded battery, make sure the cells are filled to the proper level and electrolyte level is correct.
2. Test the battery voltage. Since the batteries in many BMW motorcycles are difficult to access, you may prefer to back-probe an accessory outlet, rather than taking a reading from the battery itself.
3. Try the “rolling restart” method to check for a fault while the alternator is spinning. Anton, of largiader.com has an excellent write-up on this procedure and offers others advice on this topic, as well.
4. Use an LED probe, or make an ABS diagnostic tool to check for other error codes in the ABS system. Internet BMW Riders has articles on how to perform this procedure on several different models of bikes.
