Yburst

Hey everyone !
I just purchased a brand new audi A3 TFSI Sline three months ago. The czrs really nice, but when I'm on the Highway, after a certain distance, the brake pedal becomes really stiff and it's hard to disengage the cruise control by hitting the brakes.
I can't find anypne else on the internet with this serious problem. My car dealer couldn't find any problem neither.

Thanks

superswiss

Regular or adaptive cruise control? What trim (Premium, Premium Plus or Prestige)? Does this happen only if a car in front of you is slowing down rapidly or any time?

If it only happens if the car in front is rapidly slowing down and you have a P+ or Prestige, then what you feel may just be Audi pre-sense front tensioning the brakes to reduce your reaction time. That feels like a stiff brake pedal.

plat27265

Does it happen all the time as in consistently? If so, have the Audi tech drive with you on the highway with Cruise Control ON so he or she can experience it.

Yburst

I've got no pre-sense neither the adaptive cruise control. It's a reguler cruise control. There is no difference if there's a car in front or not.
It happens everytime over approx 15 km with cruise control on.
It feels like there is no brake assistance anymore and one must jump really hard on the brakes to get the car stop.

plat27265

Sounds like there is a very small leak in the brake booster. The leak is so small that it would take a very long time to loose vacuum pressure. When driving in the city, you use the brakes once in a while so this symptom is not evident because every time you brake, the vacuum in the brake booster is replenished. However, a small leak may cause the brake booster to loose vacuum pressure when cruising for say 15 kms without using the brakes. If there is no vacuum pressure, the brake booster isn't providing the assistance required for the brake system to function. This may explain why the brake pedals feel very stiff and hard.

Your Audi dealer will have to go through the same extended drive for them to be able to replicate this issue and confirm that it does exist. Loosing brakes while cruising on a highway at high speed is a matter that your Audi dealer should not take lightly. They should take your car for a 15 km cruise on the highway just to try and replicate this issue.

Yburst

thanks for your reply !