ABS light and Vagcom scanner

[Louis-Alain Richard]

Kneale and Victor,

There is a tiny little difference on newer cars. Modern ABS is a multi-task
system, as it is now the one that do the proportioning front-rear. There is
no hydraulic proportioning valve (dependent to the rear suspension travel)
anymore on recent cars so the rear pressure is bled internally and quietly
in the ABS module accordingly to the wheels speeds. Usually, ABS will
tolerate up to 20% slower wheel at the back before the ABS pulsing could be
felt by the driver. 

So Bentley is right : a non functional ABS will not release pressure on the
rear wheels when braking hard with the nose down and the rear getting light.
So braking force will be more rear-biased than in a normal braking, hence
the warning. If your car does have a proportioning valve, then the problem
doesn't exists. 

In my modest experience about this problem, it will show only at high
speeds, and when stomping on the brakes. But that's precisely when you don't
want them to lock... But it's probably no worse for safety than worn tires
or marginally powerful brakes. Each car will behave differently, so one may
want to test his car before concluding that it is not a safety issue.

Louis-Alain




-----Message d'origine-----
kneale at coslink.net


My 200q20v avant has been without ABS for two years because I mashed one of
the sensors replacing an axle (forgot to pull it out of its socket). 
Brakes work fine except there's no ABS, which means the rears CAN lock up
in hard braking circumstances.  Just like brakes always did before ABS.