03 trailblazer 4.2L abs or transfer case issue ?

we had a trailblazer dropped off today with complaint of abs light coming on, speedometer reading erratic & 4wd engaging on it's own. Checked codes in all modules & found c0237 in abs module & c0327 in transfer case module. Drove vehicle for over 30 miles in various scenerios & unable to get fault to occur. Customer states he had same problem 4 months ago & replaced both speed sensors on transfer case & was fine until now. The only thing that was noticed while driving & watching transfer case data is randomly the front propeller shaft rpm would read 5-600 rpm slower than the rear but no fault occured. Anyone run into this before?

I would verify speed signal to transfer case (scope) and wiggle test going forward ll wires and connectors

I don't like the C0327 at all. I'd try watching the encoder motor signal while cycling through 4WD Hi and Low. See if you can catch it glitching or sticking. Been there, done that multiple times.

The going in and out of 4WD on its own is weird. Only time I've seen that before is on an '06 Silverado, which ended up getting a reman transfer case. Excessive play in the shift fork allowed the fork to slide around on deceleration. You'd be in 2WD one moment, slow down for something, then be in 4WD! :silly:

Thanks chief for response. Thanks Tyler for your input. Customer picked up vehicle gonna drive for the weekend n see if it will occur again. I kinda of hope it gets worse so he'll bring it back so I can diagnose this one. I guess I like a challenge. Sounds like electrical issue to me? I was thinking bad wire somewhere but never got it to act up for me today. Never seen this one before. Intermittent problems can be annoying