Taos

I have a 99 4Runner that in extreme cold the brake pedal is a brick and will not stop the truck. Can barely get it to stop even at an idle. Had the fluid completely changed and bleed. No help. The brakes will start to work after the truck warms up. Extreme cold is about 10 degrees or less.

When it does warm up the brake pedal is softer and will go farther down than when it is in its cold brick, it won't work stage.

X-AWDriver

My pedal is the same way when I first start the truck but after a few pumps it's normal but the truck doesn't need to be warmed up.

GSGALLANT

Your brake booster check valve might be freezing/sticking, preventing it from opening, thus preventing any vacuum assist for your braking. Take it off and replace it with a hose nipple overnight some night that it's going to be really cold and test it in the morning to see if the problem is gone. If the check valve is the problem, try cleaning it first (with brake cleaner or something)... worse case, replace it. You should really have a check valve there though, so don't consider leaving the nipple there in its place if the check valve turns out to be your problem. The check valve being there allows you one or two pumps of the brakes with power assist even if the engine stalls when you're driving (this can be important at highway speeds). Good luck.

PS... Welcome to Yotatech... and you should fill your signature up with the specifics of your vehicle so that you don't have to keep typing them in for all your posts.