The VCDS test on the ABS is where you have to hold the brake pedal down hard, click on the 'next' button, and the brake pedal grinds away like a jack hammer. You MUST have a fully charged battery, in top condition - otherwise keep the engine running, as two complete VCDS cycles can flatten the battery!
My preferred order (get yourself a box of 6 one litre cans of genuine VW brake fluid.)
1. Pressure bleed front left, front right, rear left, rear right - until clean fluid appears. It is also good to manually press the brake pedal hard to the floor BRIEFLY two or three times whilst pressure bleeding each nipple
2. Cycle the VCDS procedure (twice if never done before).
3. Repeat number 1 (pressure bleed only, leave the foot pedal) - but wait until you get a cloud of black contaminated fluid to pass through each nipple, and wait until clear. Try to remember how long it takes for the crap to arrive at each nipple
4. Repeat number 2 again (one full cycle on VCDS).
5. Repeat number 3, and hope no more crap appears!
Then change your brake fluid every year, but start with the VCDS cycle before pressure bleeding.
As for the rear calipers, it is well known that the TRW supplied ones are pants - not just on VWs, on any other marques they are fitted on. If you are competent, ideally get a pair of spares, and strip them down yourself and refurb them. Get a good quality magnifying glass to check the smoothness of the piston bores. I have seen many supposedly 'factory reconditioned' TRW calipers with scores on their bores!
HTH
