Spongy Brake Pedal on Seat Altea

That spongy brake pedal feeling coupled with low fluid definitely points towards issues within your brake system. First thing, visually inspect all your brake lines for any signs of leakage. Trace them from the master cylinder all the way to each wheel. Pay close attention to the connections and any areas that look corroded or damp. Are you noticing any fluid accumulating near the wheels or under the car after it's been parked for a while? Also, when was the last time you had your brake fluid replaced? Old fluid can absorb moisture, which compromises its effectiveness and can lead to a soft pedal.

Thanks for the quick reply! I'll check the lines as best as I can, though space is a bit tight. Regarding the fluid replacement, I honestly can't remember the last time it was done. Is there a way to tell if the fluid is bad just by looking at it?

If you can't recall the last fluid replacement, it's highly suspect. Old fluid tends to darken in color. If it looks murky or has a brownish tint instead of a clear amber, it's time for a change. But the low fluid level combined with the spongy pedal really suggests a leak somewhere in the system or excessively worn pads pushing the caliper pistons out further than normal, requiring more fluid volume. Given your description, I'd strongly recommend getting it checked out by a professional. It's better to be safe than sorry when it comes to brakes.

Took the Altea to the workshop as suggested. The front brakes were quite worn, and there was a small leak in one of the brake lines, which explained the fluid loss. Got the brakes replaced, the line fixed, and a complete fluid replacement done. Cost me around 480€, but the brake pedal feels solid again. Thanks a lot for pointing me in the right direction!