2009 chevy 2500HD ABS light on

ABS error codes are not part of emissions control. Generic readers, unless updated, decode emissions errors. Autozone is one place with updated readers capable of decoding abs errors. The majority of abs errors are external; wiring damage to each wheel speed sensor, damage to wheel speed sensor, corrosion damage to reluctors (toothed wheel for sensors to detect whee speed). Abs error codes are prefaced with the letter C.

@notbroken I know they aren't part of emissions control. I was mentioning that to show that as far as I can tell, the obd2 port is ok. I'm not able to read the abs codes. Nor can autozone. Or oreilly. What could be causing my reader and others to be unable to pull up abs codes or communicate with the abs?

I have an '03 GM but never tried using my aftermarket clone of GMs Tech2 scantool. I was able to see other codes that my reader couldn't decode and program replacement remotes with it. I'm surprised AutoZone and O'Reillys couldn't read abs codes. Abs decoding is relatively new as our vehicles age and the demand is there. Perhaps a brake shop (call ahead) with appropriate scantool can read your abs codes. As you know, all communications go thru the OBD II port so abs error codes should be readable with better scantools. Other than measuring all for wheel speed sensors to compare resistances and close examination of reluctor, connections and wiring between each wheel and abs unit next to the brake master cylinder, it may be next to impossible to determine where fault lies.

Abs/tc/esc are completely separate from airbags, ecm/pcm, bcm, tcm and other electronics that may interfere with diagnosing/troubleshooting separate modules. All errors go thru the bcm and out on the OBD II port. Some circuits are separate on the OBD II port connections like canbus ( two wires for parallel comms. Original comms are serial, signals traveling on one wire with ground to complete serial comms. There's complicated wiring with electronics.

@notbroken trust me I know. Which is why I came here. Hoping someone can point me in the right direction because there's way too much with this type of thing for me to have any idea where to start. I think the ABS module might actually be toast. Had to slam on my brakes the other day and I didn't feel it try to do anything. Maybe that's the issue? I honestly haven't a clue. I can diagnose plenty of things but once it reaches Trans or abs I am way out of my league.