If all else fails... read the instructions!

[CharenteBeemer]

No doubt others have been there, done that and maybe even got the T-shirt, but a salutary tale nonetheless.

At the end of last summer's riding (served my apprentiship commuting in English weather, now an unashamed fair-weather biker in the sunny bit of France) the left hand red light on the ABS system came on. Cautiously tested the servo, dabbed the back to see if the ABS was still working and carried on for a glorious ride.

Glanced at the book of words and discovered that a rear/brake light fault could be the cause. Nope, rear light comes on, brake light works, can't be that can it? Probably a voltage drop because the battery is on its last legs.

Finally fitted a new battery (why did BMW apparently start with a battery and then build a bike around it...), but still the same fault light. Visions of vast expense due to some kind of management failure.

In desparation re-read the book of words, properly this time... and discover BMW's cunning system. Remove tail-light, test and discover one filament is duff even though it looks like everything is working!

Great relief - huge, expensive ABS failure is a €2 bulb, which is in my spares box anyway... !

Like I said - If all else fails, read the instructions! (properly)

[garr2]

But the instructions always make more sense after you've done the job.

[CycleRob]

The ABS system shows the red fault light because a bulb filament IS burned out, likely the park (a.k.a. running) light. It is then that the computer utilizes the still good brake light filament, at much reduced brightness, to function as the running light. That's why the bulb visually worked for the park/stop circuits, yet the bulb tested "open" on one of it's filaments.

The CAN-bus system on the newer BMW's does the same thing -but- it also displays the Lamp warning in the LCD and the yellow warning triangle in the dash panel.

RTFM* indeed!

*(ReadTheFnManual)