Hello to all my fellow car enthusiasts I’ll get right to the point. I drive a 2008 Audi A4 sline 2.0T and a few days ago my car's brake pedal went completely stiff. Scary situation luckily I didn’t crash and made it back to work. One of my tech buddies said the brake booster has likely gone bad. My only question is, is there a brake booster relay? I tried searching online and I can’t find the relay anywhere. I took apart the cover under the steering wheel and I only found a few relays. One is 404 and the other two are 373. I figured I’d check the relay first since that is the most inexpensive repair. But I could be wrong maybe the booster brake doesn’t have a relay? Any info on this would definitely help!! Thanks everyone