A week ago my Toyota Corolla 2019 started doing this. At first I thought it was air in the brake lines, but I changed the pads recently and it's still the same. The pedal goes down a lot before I actually feel the braking. What could be happening?
It could be air trapped in the hydraulic circuit, though typically that gets fixed by properly bleeding the lines 🚗 It could also be that the master cylinder is failing or there's a small leak in a hose you can't see with the naked eye, because you're losing hydraulic pressure and that's why the pedal sinks without braking. The safest thing is to have a mechanic check it with the car in the shop, run a pressure test on the system and drain everything properly - brake issues aren't something to mess around with, safety comes first.
Most likely you have a faulty master cylinder. If you just changed the brake pads and the pedal is still spongy, the air in the lines would have already come out with that job. What you're describing - the pedal going down a lot before the brakes actually engage - is typical when the master cylinder loses internal pressure, sometimes due to seal wear or a small leak you can't see with the naked eye.
Before you head to the shop, try this: with the engine off, pump the brake pedal several times to release system pressure, then start the engine and hold the pedal down for a few seconds. If the feel improves a bit once the engine is running, that's further confirmation the master cylinder is failing. Also check if there are any drops of brake fluid under the master cylinder or inside near the pedal - sometimes the leak is very small but enough to cause this.
It'd be unusual for something more complicated on a Corolla that age if it just started a week ago out of nowhere. The master cylinder is a repair that needs a shop, not something you can fix at home, but at least you know what to look for when you call.
Don't wait for your brakes to fail completely - if the pedal still feels that way after changing the pads, it's probably not air but the master cylinder losing pressure, and it's only going to get worse. What most people don't mention is that there could also be a small leak in the hoses or seals, so before you assume it's the master cylinder, check carefully whether there's brake fluid under the car or around the wheels - if it's losing fluid slowly, the pedal is going to feel softer and softer.
If the pedal's still soft after changing the pads, before you assume it's the master cylinder I'd recommend checking the brake fluid level in the reservoir - sometimes it drops so much that it feels like trapped air but it's just low fluid, and that gets fixed by topping it up. When the level's low, the master cylinder doesn't compress right and the pedal goes down with no resistance. If the level's fine and the pedal's still the same, then yeah, it's probably the master cylinder failing, but at least rule out the simplest thing first.
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