Been happening for a while now, at start up no brake or abs light. After a few miles both lights come on. Following a tip, I pulled the airbox and cleaned a ground cable next to the radiator. Saw a video where you pull the ECM out, cut the seal, open it up and there are 6 points on the circuit board you resolder, then use rtv sealant and reinstall. Does anyone know if that is worth trying? I looked for a sticky, but then again sometimes I can't even find my WITH a bell on it.
Also did recently replace front pass side hub amd no change in Abs light.

 

There is a code that's triggering the abs light. ABS codes are automatically cleared when the truck is shut off. Drive it until the lights come on and have it scanned with a scanner capable of retrieving abs codes.

 

The easy possibility for both lights "on" might be the master cylinder fluid level is low. IF so, it is about the easiest fix.

 

you have cracked solders in the abs module. it can be resoldered

 

I know the booster diaphragm has a hole in it but I don't think the Blazer has anyway if knowing that.

 

you need to repair the abs module, just like the video