Brake Warning indicator

[Guyj]

I have a 1992 Chevy truck w/rear wheel only ABS. Recently my brake warning lamp started illuminating on the dash. It is not on when I initially start the truck but as soon as I reach 35MPH it comes on and stays on until I turn off the engine. This condition repeats each time I start the vehicle and drive it. Last week I put a hand vacuum pump on each of the brake bleeders and bled all four brake lines. The front brakes bled normally and yielded a steady flow of fluid without air. When I bled the rear brakes I got very little fluid from them. There was a lot of air being pulled through the vacuum pump but I believe it was coming from the threads of the bleeder valve and not actually pulling air from the brake lines.

This morning on the way to work the brake light came on at 35 mph as usual. But after stopping at a light it began to flash. It would flash 9 times and the tenth time it would stay on for about 1 sec.This condition repeated all the way to work until I turned off the engine and the warning light went away as usual. Is the flashing a trouble code or is it just a higher level warning than that of a constant warning light? Any ideas what causes the warning light? I suspect it is something to do with ABS since the warning only comes on at 35 MPH and my Cruise control quit functioning when this started happening. My brakes are spongy but I have no problems stopping. The sponginess made no change after the brakes were bled.

 

Guy