I'm hoping somebody can help me figure this out.

I have a 2001 F150. Front brakes replaced a few months ago.
Last night, I realized my rear brake lights weren't working. I'm not sure how long they've been out or if it's related to the bigger problem.
While testing the brake lights by pressing the brake pedal, the pedal seemed to give out and sink lower.
While driving the brakes worked but only when I pushed the pedal all the way in. Eventually the ABS light came on and stayed on.
Any advice?

 

I don't have the same exact problem, but my ABS light stays on with no codes. My mechanic is tearing his hair out trying to figure it out.

 

Sounds like OP has a leaking cylinder, caliper or brake line----could also be related to the master cylinder.

Check for visible signs of a blown cylinder/caliper or leak, fluid all around or even on the ground. If nothing there it might be time to check both the brake booster and master cylinder. Most likely the MC but good to check both anyway.

 

Your mechanic may need a better scan tool.

The OP posted several months ago and hasn't returned to the web site in more than a month.