"service Brake System" Error Message

[adam_murphy]

Got this message yesterday while pulling my trailer. It seems to put the truck into limp mode, not having any gears but 3rd, as well as illuminating the ABS light and the "BRAKE" light. If going under 15 mph, the lights and message will go off, hit about 20 and the speedo goes crazy moving all over the place, and it goes into that limp mode again. One code was for the front wheel speed sensor and another one was for another sensor, cant remember off hand. Is it just ironic that the wheel speed sensor code comes up when the xfer case decides to give me problems? (see other thread in this section for that) Has anyone else had this problem? I've checked all grounds, all fuses, everything.

[95Sierra2500]

I'm guessing you just had a wheel speed sensor take a dump on you. For my old '95 they are $250 a piece. I don't know what it'd be for your truck. That's where I'd start though. There's a write-up somewhere, I'm sure, on how to test them to make sure yours is actually bad before you replace it, but I"m not sure what the values are and everything.