The other morning when it was very cold here when I fired up the truck the ABS and both the brake warning lights in the dash stayed on. checked things out and then carefully drove to work. I figured I would check it out when done work. Anyway the truck sat in the shop all day nice and warm. couldn't find anything wrong and lights all went out as usual. Next morning same thing. early morning temps at about -28 to -35 C. when truck sits in the warm shop no lights. this morning it was about -14 C and everything was fine. Any ideas.

 

DO a search lots of reading.Could be sensor on rear axle,vaccum line by battery or vaccum switch on fender by firewall on driver side.I had the same problem except it was my rwl box under dash.Does your truck shake some when you hit the breaks hard? I tell you how i fixed mine if you pm me can't post it rules
tom