A8 brakes coming on by themselves...

[Mark_Derry]

Hi Guys,
Can anyone help...

A8 4.2 TDI Reg Jan 2008

This was not the case when you go down hill and the breaks gently apply to keep the car to it's set cruise control speed.

Whilst travelling at about 50 a warning light came on and soon after I notice some slight resistance to forward travel.
A few seconds later I notice a thin wisp of smoke !
So I came off the throttle completely and noticed the car slowed up as though I was putting gentle pressure on the brakes.
I immediately pulled off the dual carriageway and came to a stop within a few seconds.
I shut everything down and got out for a visual inspection.
This showed both front discs glowing red hot.
The brakes hadn't come on hard but might have been on too gently to notice for a while.
I let everything cool off and called a flatbed to recover me.
A couple of hours later they turned up and I started the car up to align it for loading.
The brakes were not locked on but now spongy - I figured the excessive heat would have boiled off the brake fluid.

My mechanic has looked at it and said all four brakes had been on, not just the front two.
The rear disks weren't so hot when I'd stopped but most braking force goes through the front brakes.



My mechanic says the master cylinder


and servo have destroyed themselves but has no idea what might have caused this to occur.

Please can anyone let me know what might have happened here ?
Ideally if anyone has experienced the same failure, please can you point me towards the probable cause...

Many thanks
Mark

[Cupramax]

No idea but for all four wheels it sounds like the ESP or ABS may have shat itself. As with all things Audi get the fault codes read first and see what the car thinks is wrong.

[WinstonWolf]

Could be an EPB fault, as mentioned get the codes read.

I'm surprised the master cylinder/servo are toast, I'd expect the collateral damage to be to the friction components unless the master cylinder has failed causing the initial problem.

[Mark_Derry]

I suspect these haven't been cleared down for a few years....
Codes appearing are :-
ECP
P161A Glow plug
P1653 DTCABSCM <- not too sure what this one is...

Brakes
01435 Brake Pressure <- I suspect this came as a result to the failure not the cause

Kessy
00955 Both keys <- maybe they need new button batteries
00956

AC
01857 left central vent sensor

Central Elec
02510 Steering Col Adj

Engine Control Mod 2
P1573 Left Electro-hydraulic engine mount
P161 No 3
P161B No 8
P161E No 5 glow plugs

Parking Brake
01316 Brake Control module <- this is my prime suspect, what do you think ?
02596 Rear Brake linings worn

[Cupramax]

Yes, basically the ABS ESP controller, what I said.

[WinstonWolf]

01316, the EPB can be deployed at speed (don't!) It will exert full braking force on all four wheels even at speed.

[Mark_Derry]

WinstonWolf said:

01316, the EPB can be deployed at speed (don't!) It will exert full braking force on all four wheels even at speed.

I didn't deploy EPB (in fact I hardly every use it at all)
if it had failed and deployed itself I'd have expected the car to brake hard, whereas I experienced gentle braking not hard braking.

[Mark_Derry]

What about P1653
could this have caused it ?

How would one set about confirming which module had caused this failure ?
I don't want to spend four figures fixing all the bits that broke following this failure without being sure I've identified the cause and then hit the same problem again a few days later...