Brakes Go out under 5mph then lock.

Just a feel thing? Did you get the ABS flash done?

 

Worn brake pads.

 

pump the brakes

 

Under 5 mph, it switches to friction braking. Is that what you're feeling?

 

could there have been ice on the discs?

 

I have had this happen to me once. The big question: did you have any lights go off and or beeps?

Last year about this time I hit a sharp ridge of ice about 3-4" high approaching a heated crosswalk. As soon as I hit it (about 10-12 mph) my brake pedal sank to the floor (bottomed out) and warning lights went off and beep twice. I came to a stop half way through the walk. Scary. I took it in for the ABS update and have not had it happen since.

 

Most likely your friction brakes were icy or dirty. They don't get much use on a Prius, and as a result often end up a bit rusty or dirty, especially if you drive in winter conditions or near salt water.

You might want to try cleaning the brakes by forcing them to work. Try this on an empty road:

1) Accelerate up to about 45 mph.

2) Shift to N.

3) Brake until you are going around 20 mph.

4) Shift to D.

5) Repeat.

Do this a few times and see if your brakes don't feel better. It will wear off some of the rust and dirt.

Btw, if you are a software engineer, systems person, or Canadian, stick a loop counter and escape clause in that loop; otherwise you will be stuck there until your Prius runs out of gas.

Tom

 

What about some air in the brake lines, which would only show up below 6 mph, and might be sporadic depending on temperature??

 

We have air brakes?!? Wow

 

A bubble of air in the brake line fluid.

 

The OP described it as running out of pedal travel, as in the brake pedal going to the floor. Rust or dirt accumulation would do the opposite, the pedal would be higher than normal and feel firmer.

Sounds more like worn out pads, fluid level problem, or electronic malfunction. Take it to the dealer ASAP. Make sure they write up the complaint and symptoms in case you have more problems in the future.

 

You've got to take the car to your dealer for brake system inspection. As folks have said it can be anything from nothing to brake cylinder to dirt. Get it checked out.

 

Agreed, but ice would do the opposite.

Tom

 

The symptoms you described are scary at best. I feel a defined transition from regen. to friction brakes around the 5-7mph mark with my 2010 since new. As the car approaches the transition speed while I apply brake pedal pressure constantly and smoothly, the brakes feel like the stopping effectiveness is steadily decreasing and I will never stop in time. To combat that occurrence I press harder on the pedal and when the friction pad finally engage, the braking rate dramatically increases and I come to an abrupt stop. I try to stop smoothly with all of my cars which seems impossible with the braking system design on the GIII.

At this next oil change I will bring this up with the Toyota tech people but you know how that is going to go.