E46 - weird brake problems

that's a tricky one! I think it will be best to take it to a main dealer or specialist to get the computer plugged in first to see if there any codes etc.

Next to take caliper off and check pistons/pins for free movement.

Good luck!

OK, I thought since I had asked you all for answers, I'd give you the end of the story.

I got the fault codes ready by a local indy and nothing showed up.  However, I was scratching my head with the bonnet up on the 325 and the CSL back to back and noticed something that should have been obvious to me all along.

I knew that my car had had work done in the right front area as a result of an accident, but not much more than that.  As it turns out, the DSC/ABS unit had obviously been removed and either replaced or refitted at some point and the pipes had been connected incorrectly on refitting!  There are two feeds from the master cylinder and one of them was interchanged with the take-off for the rear left caliper.

As far as I can tell, this meant that the brakes felt OK when under normal use but th emoment the ABS engaged the total pressure from the master cylinder was channelled to the rear left caliper, with no electronic interference at all!

That was easily remedied once I knew what I was doing.  It is a shame it toasted a nearly new rear tyre though, as the 255/35/18's aren't exactly cheap!

Thanks for all your ideas and sorry for not updating sooner.

holy crap!