OK, I trust we all know the brake fluid must be changed every two years (at least).
And I also trust that some may also be aware that main stealers are supposed to hook up the VAS5051/5052 electronic diagnostic dooberys to 'cycle' the ABS/ESP unit, and that this can also be done with VCDS.
Now, I reckon many peeps (and indeed many main stealers - because they obviously didn't on my GTI
- detail later) don't bother cycling the ABS/ESP when renewing the brake fluid.
Until now, my personal advice - for those of you who bleed your own brakes, was to try
to use VCDS, but that it wasn't vital. I've previously suggested to bleed the brakes using one of the conventional methods (either two-bod pumpy-pumpy, or with a one-man pressure bleeder), and then take the car for a spin, and 'exercise' the ABS/ESP systems (by doing a few hard stops on a slippery surface to activate the ABS, and a few wheelspins to activate the traction control). And then go back and re-bleed the brakes. And this was what I had previously done myself.
However, on my last brake fluid change, I did some experimenting. I bled the brakes using the trad two-man pumpy method (200ml from left front, right front, left rear, right rear - then another 200ml from all four again). I then hooked up VCDS and activated the relevant ABS functional tests (to activate all four individual circuits for 30 seconds) - and then bled all four again. I was SHOCKED with the really black
fluid which then came out. It was clear to me that the fluid had been going stale in my ABS/ESP for four years.
Now, the morale of this experience is very valid. All VAG PQ35 platform cars (Golf Mk5, 8P A3/S3, TT Mk2, Leon Mk2, Octavia Mk2, Passat B6, Touran - and prolly some I've missed) all use a Continental Teves Mk60 ABS/ESP unit. These Teves units are well-known to be unreliable. The Touran forum is rife with real failures of these, costing owners £1500 to replace. Many BMWs also use these Teves units, and again, are well-known to be very unreliable (especially when compared to the Bosch units which longitudinal Audis and Mercs, and Vauxhalls use).
So, I very strongly urge you all that you MUST activate the ABS/ESP unit via VCDS when changing brake fluid.