My brake/abs problem didn't bring the warning light on but due to the 'cheap' pads no matter how much brake pressure I applied the abs wouldn't work on the road as the pads weren't gripping the rotors enough. If I tried it on gravel/loose surface or cobbles/shiney surface the abs worked fine. Fitting standard pads brought everything including the pedal pressure back to normal. (My mechanic did originally leave the rear, I think, abs sensor rings off which did bring the light on & confuse us even more for a while though!).
Thanks to 'twistedsymphony' for the tutorial on braking systems but new cheap 'bad pads' can cause pedal pressure problems.
Clive