iABS woes on a K1200RS (somewhat long, sorry...)
OK so here's the story:
I have a K1200 RS, picked up last September (2017). It has been showing intermittent failure of the rear brake servo (iABS partially integrated is fitted). I have tried the following:
Change of all brake fluid by trusted independent BMW mechanic. And then made sure DOT4 fluid in all 3 reservoirs was topped off to the max, myself, just to make sure.
Checked resistance of front and rear ABS sensors. All good.
Checked continuity of front and rear brake switches. All good.
Checked (and then changed anyway) rear brake/tail bulb.
Checked load at starting on battery. All good.
Hitting the unit with a piece of wood and an extension bar (the theory being I could unstick a sticky pressure relief valve, seen on photos/schematic by people who've actually dismantled the things). This would work for any distance between 200 yards and 20 miles before the rear servo stopped again.
Trusted independent BMW mechanic says: Unit buggered probably, take it off and convert to hard non-ABS brakes. Main BMW dealer says nothing we can do, you probably need a new mega-expensive iABS unit, but we'll clear the faults off the computer for you (as the brake system is working when I visit them, obviously...)
Since BMW dealer cleared the computer... No problems. iABS unit works perfectly.
My question is, why? The only possible answer I found was on page 267 of the Clymer manual, where it says (in the bit about the Throttle Position Sensor reset):
'...if any fault codes were set before the battery was disconnected, they will be reset as soon as the motorcycle is ridden a short distance.'
I first saw the intermittent failure from the bike when first riding it, and noticed that, although the bike was in good condition generally, it showed definite signs of having been left standing still in the elements for too long.
And I disconnected the battery twice to fit things like Optimate cables, and check connections were good. Have I been basically 're-awakening' old fault codes every time I get on the bike? Is that the reason for the intermittent failure? Now the bike has been used a bit, and had its fluid changed, do the brakes actually work fine, but with the 'ghosts' of old fault codes deciding to cut out my rear servo? Why should a simple clearing of the old fault codes lead to such a dramatic improvement (over 100 miles trouble free, which hasn't happened in ages)?
Do any of you fine people know the answer? Despite being blessed with both an independent BMW mechanic, and a main dealer within a few miles of me (I'm in the small UK), knowledgeable guys on the web have managed to give more tips than them and the Clymer manual combined, so far. Thank you for reading this far, in any event!
PS: If anyone knows how to 'hack' the iABS unit electrically (using connections at the diagnostic plug, for example), I'd be interested to know, as the rest of the internet seems to think it's impossible!