Symptoms:
- When car is first started, pressing the brake pedal feels normal.
- After driving for a short while (often less than 10 minutes) the brake pedal progressively sinks all the way to the floor under even very light pedal pressure, and the brakes become less effective. Eventually they may stop working entirely, though there is still some minor braking effect. There is no fluid loss from brake lines.
- Pumping the brakes repeatedly does not seem to help.
Troubleshooting steps:
1. Check brake fluid level - Full
2. Look under the car for leaking brake fluid- None found
3. Inspect pads and rotors - All look fine
4. Check for a vacuum leak - None found
Mechanic's notes:
- Customer reports that sometimes turning the engine off while stopped does resolve the issue, and brakes will be responsive again when the car is restarted. However, the problem recurs after driving for a few more minutes.
- Pressing the brake pedal to the floor and holding it while starting the engine also temporarily resolves the problem, but again it soon returns.
- Applying light foot pressure to the brake pedal while driving causes an immediate loss of brake pressure, and the pedal travels further towards the floor. If foot pressure is kept constant, brake pedal pressure steadily decreases until reaching the point where the brake barely works at all.
- Applying heavy pressure to the brake pedal (enough to cause a little wheel lock up) sometimes results in the brakes working normally again for a short time, but the issue returns soon after.
Question:
What could be the cause of this problem, and what steps can be taken to fix it?
