Thought i would share this experience just incase anyone else has a similar issue.

Left home couple of days ago and as I pulled away and dropped of the kerb it felt like something changed on the vehicle and performance felt sluggish. Kept going for a mile or so but it didn't feel right so pulled over. As i did I got assaulted with a full set of bongs and lights including ABS/HDC and a HDC Innactive error in the dash.

Did the normal of "turn off/turn" on but bongs still there. Plugged in IID (never leave home without one ) and tried to clear errors but made no difference. Can't remember the exact errors but if I recall correctly it was saying it couldn't find the Cruise Control/HDC/ABS. Went to drive home again and the brakes were set on pretty firmly

As I had only pulled over on the side of the road I wasn't in a safe place I ended up driving against the brakes to get it properly off road.

Spent a while checking fuses, trying to reset errors on IID, all to no avail. Eventually called out recovery as the car was undriveable with the brakes on

Whilst waiting for the flatbed to arrive had a bit of a Google and search on here and a number of posts mentioned that the HDC inactive/Cruise Control errors are often as a result of ABS problems as the systems are all linked. I was trying to think of what could be different/caused the problem and remembered that the day before I had been changing a couple of injectors and had been leaning over the strut tower and ABS pump.

So I decided to check out the ABS pump to see if I had disturbed anything..... Nothing obvious but thought I would pop the multi plug as I had had problems with BMW multiplug's on my previous 7 Series. You release it by pulling forward the end then it levers up

Just as an update on this, I had the same problem again in the snow after an extended ABS event on ice (no drama's all nicely under control, just a bit slippy )

Anyway, all the bongs and brakes locked again. Eventually got to release after a battery disconnect and mucking about in the freezing cold for 30 mins

After that the soft brake pedal was even worse and it was obvious the master cylinder was toast, sitting with foot on brake and engine running pedal would go to the floor relatively quickly and go all the way down, then there would be no brakes. Much more pronounced than the normal very slow "give"" in the pedal if you hold your foot on it with the engine running.

So at the weekend I replaced the master cylinder. Pretty straight forward:
1. used a suction device to lift fluid out of the reservoir
2. lift two plastic clips that secure reservoir to master cylinder and remove reservoir - note it is very "Tight" as the plastic spigots push into rubber bungs on the top of the M/C, takes fair bit of wiggling and effort to work it out and it is a pain doing this whilst trying to stop the plastic clips from re-engaging!
3. remove rubber pipe to pre charge pump and cap it off.
4. disconnect 3 brake lines from M/C and cap
5. remove two nuts securing M/C to servo

All the above covered in RAVE.

I don't have access to Testbook and the normal IID BT doesn't seem to have the brake bleed/purge routine so I proceeded as I would for a "normal" car.....

1. Fit new M/C to servo making sure the actuator rod slips into the sleeve on the M/C and bolt up
2. With brake lines disconnected pour new fluid into two ports on top where the reservoir fits, it will take a small amount but it won't run out of the brake line holes
3. Fit reservoir and fill
4. Get willing assistant (wife wrapped up in 16 layers as it was -1 in garage ) to gently squeeze brake pedal until fluid starts to seep out of 3 ports. This didn't happen all at once so I reconnected the lines to each port as the fluid appeared.
5. When all 3 lines are re-attached, loosed off 1 line at a time and press pedal till no more air/bubbling
6. Repeated with other 2 lines.
7. Bled all four wheels fully to flush completely new fluid through system (much easier if you have a vacuum bleeder like I have as you can just connect it up and it sucks the fluid through whilst you keep the reservoir topped up )

This approach seems to have worked a treat. I realise it wont have pushed new fluid through all the ABS pump etc, but by capping the pipes I think it stopped the system fully leaking down or getting air in and then bleeding the M/C then all pipes has cleared any air out of the system.

Took it for a couple of drives and nice hard pedal now, also played on the latest snow and no probs with ABS actuation.

Original problem of locking up after ABS actuation hasn't recurred but time will tell. It could have been a pressure sensor issue caused by the leaking M/C (he says hopefully) or could be an ABS sensor/Steering sensor problem, or a sticking valve in the ABS pump/block.

But here's hoping it was the simple cure!

Cheers,

Paul 2011 TDV8 AB
2006 TD6 AB (Gone to Wales)