ok so my rotors were bad so i decided to change them instead of having them cut so i change the 4 rotors and brakes all around take it for a test drive about 1 mile on the highway on the return trip as soon as i get off the highway my brake light comes on and the pedal goes all the way to the floor i didnt mess with any sensors or calipers just a simple rotor and brake change ..mind the brakes where working fine before this...what could be the reason this could happen...please help

Did one of the brake lines come loose or crack after your brake job? I guess I should of asked if there is still brake fluid in the master cylinder? The light usually comes on due to low fluid.

You probably cracked/broke a brake line at one of the wheel cylinders when you lifted the caliper out of the way to pull the rotor. Look behind each wheel and on the road/driveway for leaking fluid, and check the level in the brake fluid reservoir at the master cylinder.

Also check the calipers themselves. Sometimes if they don't get compressed properly, you can pinch the caliper, and a leak develops. I agree though, look for leaks, that is likely the cause.

yes thanks everyone it was a pin hole leak in the rear brake line after further inspection I notice the brake lines were very rusty..so just going to change all 4 lines looks like a pretty tough job so going to let the shop deal with this one...thanks for all the help

thanks for posting the fix

I'm so glad I don't live in the rust belt.