carguy5760

Just purchased a 90k mile 2008 S8 about a month ago. Love it. My mom has a 2005 D3 A8L, and I've had a 2009 S8 before, so pretty familiar with this car.

Parked it for 2 days outside in the New England Cold. Went to unlock it. Alarm went off. Eventually stopped. Got in. Started car. All electricals going crazy. Everything turning on and off. Lights flashing. My guess: low voltage. So I pulled it in the garage, disconnected the battery and charged it overnight on my NOCO slow charger.

Next day I reconnect the fully charged battery (which was relatively new) to the car, start it and drive it to my local Audi dealer. I ask them to diagnose the low voltage issues (I suggested that maybe the battery was replaced by the previous owner but not coded), change the oil, and give me a full inspection of the car. I get a call back two days later. They said I was right. Cleared all the codes for low voltage, coded the battery, changed the oil and said it was a great car. They billed me $300 and sent me on my way.

Two days later I notice the car sitting low on its airbags. My first thought is - perhaps a leak bag, one way valve, or overburdened pump is what caused the battery fail? I drive it back to Audi dealer, and on the way there, I notice the car braking on its own when I release the brakes. Very noticably. I drop the car again at the dealer and tell them about the car dropping on its suspension, and about the self braking. I get a call about a week later. They want to do a one way valve that is leaking in the air suspension, and suggest rebuilding all four calipers and doing a brake flush. I approve the work. Two weeks later (today) I get a call from the dealer. It appears the air suspension is holding, but the tech took the car out today and it is still self braking. Now the dealer wants to sell me a master cylinder and brake booster for $1800. I'm looking for second opinions here.

I scoured the internet for D3 self braking issues and outside of calipers sticking, cant see any booster/master cylinder replacements. It does not look like a common occurence. I also question the timing and never think anything is a coincidence. Could there be anything electronic that could have failed or blown a fuse as a result of the low voltage that would have affected the brakes? Any ideas are sincerely appreciated.

Matt

Giovanni Giovino 6.0+6.0TT

Hello Matt, Welcome Aboard !
As far as the self braking, is it front or rear, or all 4 corners, does your 2008 S8 have Adaptive Cruise Control (ACC applies the brake at certain following distances) , also I do not see how the master cylinder would have anything with the brakes self applying, also if the brake booster was bad I would think it would be a vacuum leak, which in turn would give you a stiff brake pedal, now on the other hand, how about a faulty ABS module, or parking brake module, does anyone here think either of those could in anyway cause the brakes to self apply ?

Did they give you a scan readout?
.

carguy5760

Thanks for the quick reply.

I don't think adaptive cruise and side assist were available on the S8 til 2009. Pretty sure this 2008 doesn't have them. Even if it did, its braking with or without cars in front of it. It brakes on its own from highways speeds or coming to a low speed stop.

Pedal stiffness is normal, and no vacuum leaks according to the dealer. The dealer also says no ABS faults in the system.

PaulW

The adaptive cruise control can be seen below the front plate, the grill is not complete at that location, this is the radar unit.

This car doesn't have it....but it has a RED paint job!
I agree on the adaptive cruise control, do you have a picture of the front of the car you can post? On my car you can see it has the ACC just over the bottom part of the front grill and the red car does not have it. If you do have it....I would say that it is this system going crazy. When it brakes on you, it can brake HARD. First determine if you have it or not. I would stop the madness at the dealer and spending money. I would hate to know what they charged for rebuilding the calipers.

carguy5760

carguy5760

Jack88

The dealer has no idea, they are diagnosing it by throwing parts at it. I've never heard of this issue, it's very strange. My first guess would be sticky calipers, but if they have been rebuilt, it's hard to say what it might be from there.

PaulW

Could you please be more descriptive regarding the brake issue. When does it do it? When you are on the gas, off the gas or on the brake?

How hard does it brake? Light? Heavy?

Does it just jam the brake on with no warning?

Any lights on the dash before, during or after?

Is it more prevalent at high speeds or low speeds?

Do you have any more lights of any kind per your first post above?

RobertV

My 08 A8L, which doesn't have adaptive cruise, brakes going down long hills when the speed is higher that the set cruise speed. Is it possible that there is an issue with your "standard" cruise control or one of the sensors? On mine the brake lights light up and the car slows down to the set cruise speed. Just something else to think about.

carguy5760