Q: Brake pedal goes to the floor when the engine is on

The first thing you’d want to do of course is pull off all the wheels and look for the leaks. But if you have no leaks, yours is the classic sign of a bad brake booster. When brake boosters go bad, you step on them with the engine off and will notice the pedal is nice and hard. When you start the engine, they go right to the floor. If this is what you are seeing, it’s probably a brake booster. But check for leaks first because brake boosters are pretty expensive and are no fun putting on. If you want to have to have this looked at first, a technician from YourMechanic can come to your home of office to inspect your brakes and replace your brake booster if necessary.