Avalon brake goes to floor before starting

My stepmother has an intermittent problem on her 2006 Avalon with keyless system. She must put her foot on the brake in order to start the car. On occasion, the brake pedal goes to the floor & car will not start. On second try, pedal goes about halfway, and on third try, there is full pedal and car starts. She’s taken it to Toyota twice and they can find nothing wrong. It happens every month or so, but never happens while driving, thankfully. However, I am worried that this is a serious problem, maybe master cylinder failing? Has anyone experienced this problem?

I would bet that the master cylinder is worn internally and the fluid slips by the seal on the piston when the car is cold. It is a serious problem because she may not be able to stop the car sometime while she is on the road. I think for safety’s sake, the master cylinder should be replaced.

Ditto.

I strongly urge that she not drive this car until it’s repaired. While the master cylinder can be bench tested, I emphatically suggest that it simply be replaced amd then use bench testing just as a confirmation if you’d like. I’m not normally just a parts-changer, but the risk in this case is so great that it justifies changing the MC even if the problem cannot be verified in the bench.

Please, I urge you, get your stepmom to have this car towed to a shop. Left unrepaired it will be a tragic accident looking for a place to happen.

Does she also experience this problem in normal braking, or just when starting the car?

Only when starting the car