99 yukon 2wd. 5.7/4l60. 0411 ecu swap. mpfi. stock everything else.
front brakes are locking up easily, very pronounced with a load on the hitch.
(!) (P) BRAKE light on dash on. ABS light not on. no stored ABS codes when read with tech2.
assume parking brake switch works because it turns off the DRL dash light when pbrake is pushed in.
with the abs fuse in they alternate, with the abs fuse out they both lock at the same time.
tech2 shows all 3 wheel speed sensors to be the same speed when rolling down the road.
I just swapped back to a new OBS master cylinder from the NBS MC I had installed a couple years ago, just in case that was the issue. no change.
replaced the front lines and calipers at the same time as I installed the NBS MC.
the brakes worked good for a long time after doing the NBS swap.
replaced the rear cylinders, drums and shoes recently after I noticed the issue. had one blown cyl and the shoes were worn out.
I have done ABS bleed with tech2 multiple times
if I unplug the wire to the ABS module, the dash brake light turns off. symptoms remain.
I will be putting the truck in the air to flush the fluid some more and check to see if either of the rear cyls are leaking. not sure what else to do.