What does 'Audi A3 brake assist function restricted' mean?
2 Answers
Brake assist system restricted refers to the failure of the brake assist system. It is necessary to check whether there is any air leakage in the vacuum pump or pipelines, and also to check whether the vacuum pressure sensor has malfunctioned. If a fault occurs, it should be repaired in time to avoid accidents. The working principle of the brake booster pump is as follows: 1. Air intake: The brake booster pump uses the principle of air intake during engine operation to create a vacuum on one side of the booster, generating a pressure difference compared to the normal air pressure on the other side. This pressure difference is used to enhance the braking thrust. Even if there is only a small pressure difference on both sides of the diaphragm, due to the large area of the diaphragm, it can still produce a large thrust to push the diaphragm towards the side with lower pressure. 2. Working state: In the working state, the push rod return spring keeps the brake pedal in the initial position. At this time, the one-way valve at the connection position of the vacuum pipe and the vacuum booster is open. Inside the booster, the diaphragm divides it into a vacuum chamber and an application chamber. These two chambers can be connected to each other, and most of the time they are isolated from the outside. Two valve devices can connect the chambers to the atmosphere. 3. Engine operation: When the engine is running and the brake pedal is pressed, the vacuum valve closes under the action of the push rod, while the air valve at the other end of the push rod opens. After air enters (which causes the panting sound when the brake pedal is pressed), it creates an unbalanced air pressure state in the chamber. Under the effect of negative pressure, the diaphragm is pulled towards the brake master cylinder, thereby driving the push rod of the brake master cylinder, which realizes the function of further amplifying the leg force.
I encountered a similar warning when driving my Audi A3, which actually indicates a problem with the braking system. Simply put, the power assist device that helps you brake might be failing. There are three common causes: a vacuum hose leak can prevent the booster pump from drawing enough air; a malfunctioning sensor might falsely report a fault; or the brake fluid could be too dirty or low, leading to insufficient pressure. You'll notice the brake pedal becomes stiff, requiring much more effort to stop the car. I remember once during a heavy rainstorm, I faced this issue and was so scared that I immediately turned on the hazard lights, pulled over, and restarted the car to resolve it—later, it turned out to be a faulty sensor. If you see this warning, don't push your luck; slow down immediately, pull over safely, and check the system.
