What is the reason why the BMW ignition brake cannot be pressed down?
3 Answers
BMW ignition brake cannot be pressed down due to problems with the brake hydraulic system, causing excessive pressure; the newly replaced brake discs have not been adjusted, resulting in the inability to press down. Brake hydraulic system failure: The car's vacuum booster pump leaks or malfunctions. The force applied to the brake pedal is amplified by the brake booster pump. If it fails, the brake loses its assist, making it difficult to press down. Newly replaced brake discs: New brake pads require a break-in period of 200 kilometers to achieve optimal braking performance. Therefore, it is recommended to drive cautiously after replacing new brake pads.
Last time I encountered a similar situation while driving, the brake pedal felt welded shut and couldn't be pressed when starting the car. Later I learned that BMW's vacuum booster slowly loses pressure after engine shutdown. If you press the brakes after turning off the engine, the remaining vacuum gets depleted, making the pedal extremely stiff before ignition. But normal vacuum assist resumes immediately once the engine starts running. If the pedal remains stiff after starting, there's a 90% chance it's a vacuum system issue - possibly a leaking booster pump, cracked hose, or stuck check valve. During previous repairs, I noticed older BMWs often develop vacuum leaks at intake pipe connections. Don't force it - call a tow truck immediately to inspect the entire booster system, as this directly affects safety.
I've studied BMW's braking system structure, and this kind of 'can't press down' situation is mainly caused by the vacuum booster. Think about it - after the engine is turned off, the vacuum pump stops working, but there's still some vacuum left that allows you to press the brake pedal easily a few times. If you use up these few presses or don't drive for a long time, the remaining vacuum leaks away, so naturally you can't press it when starting again. But once the engine starts, the vacuum system should resume working, so the key is to check whether it returns to normal after ignition. If it still feels rock-hard, there's an 80% chance it's either a broken vacuum line or a faulty check valve. Older BMW models using rubber tubes are prone to aging and cracking - this needs professional equipment to test the vacuum level. By the way, rubber components tend to harden more easily in cold winter temperatures.
