I've been dealing with my 99 Blazer LT 4x4 transfer case 236 AutoTrac for about 3 months now trying to diagnose and fix it by myself through the help of forums and similar and am still stuck with the same issue: no lights on the 4x4 switch.

I've replaced the switch, bought a TCCM off Ebay and have done a lot of multimeter testing which is somewhat hard to troubleshoot when I don't have a lot of doco to go off. It started off about 3 months ago where the lights on the dash would sometimes not come on when the vehicle started up, when they did 4x4 works perfectly without an issue. Between the start of the issue and now the lights started to work less and less, 90%, 50%, 20%, and now never and of course we're in winter now .

Fuses are good, replaced them anyhow, the TCCM wires appear to be fine now and not corroded, I cleaned them off a bit. Right now I'm thinking since I replaced the switch (brand new) and replaced the TCCM (Ebay, could have been bad), that maybe the encoder motor is bad. Unfortunately I cannot ground PIN13 as this is a 236 Tcase and I'd rather buy a part for 20-75 so far instead of paying 100.00 to diagnose with a tech2 scanner.

This is what I have right now. Previous to replacing the switch with the brand new one the 4x4 dash light near the speedo came on when the ignition was turned on like it should, now it doesn't. This is also true for the 4x4 button lights, they don't do anything at all now either, great huh. What are your thoughts? I tried to clear the TCCM a few times and the same issue comes up. I also would have just made it a manual system, but it appears I cannot on a 99.

Any thoughts on what is wrong or troubleshoot tips to figure out if the TCCM is working properly or the encoder motor is good? Could I test the lines down at the encoder motor to see if the 5V on the encoder lines are there with the encoder motor electrical connector off or does that make the TCCM not work, doesn't seem like it would?

Thanks for your replies and I know they're are similar issues on the forum and Google and well I've looked at all of them pretty much.

 

Read this thread, we've been working the same issue. I had mine fixed for a little over a week and it went dead again, so I'm back to square one, but if I do get it figured out I will update. Current issue is getting it scanned. My sister cannot spend 100.00 to get it read.

https://blazerforum.com/forum/2nd-generation-s-series-1995-2005-tech-41/1999-lt-blazer-4x4-auto-4x4-problem-wont-shift-all-shifts-its-own-52230/