I've searched for something related to my issue, I believe I'm having a mentally vacuous day because I've not been able to fix the issue. 2001 Blazer with NV236 (4 button) . I can get it to 2wd, not sure what I did, messing with output hose and electrical connector on Vacuum switch on the firewall. From there I can drive in 2wd, stop, restart, still 2wd. I push Auto 4wd button, light flashes as it switches, then solid light, and I seem to be stuck in 4wd, not back and forth, even on clear roads. Will not switch back to 2wd when button is pushed, cant get 4hi or 4 lo buttons to do anything either. Took out battery and tray, cable moves free and easy, does not appear to be stuck, corroded, or broken. When I pull out bottom vacuum hose on Vacuum switch, I can hear the air. Disconnect air line and electrical connector, plug hose back in and then electrical connector, you can hear quiet click or clunk, I think its back in 4wd, even though I'm not moving. Biggest hope is to be able to push "2wd" button on dash and switch back to 2wd. Sorry I went so long, hope I provided eneough detail.

Update, just disconnected both harnesses from TCCM, started, ran forward few feet, reverse few feet, no lights on to indicate 2wd, auto 4wd, etc. Shut off, reconnect all, start up, without me pressing any buttons, starts in 4 HI. Pushed 4 LO, 2wd, got nothing, pushed Auto 4wd, went to Auto 4wd. When I say "nothing", light does not even flash like it is trying to go into 2wd or 4 LO.

 

Have you tested the switch resistance? All of the wiring to/from the TCCM/switch/encoder motor? The wiring & other details can be found in the Tech Article (DIY) section; an index of which is linked to in my signature below.

 

Thank you!! I will check it out and let you know what was wrong.

 

Swartlkk, Thanks for the help. Dash switch resistance value for "No button pused" is way off, reads as if 4HI is being pushed. I'll replace switch tomorrow.

 

Swartlkk, That did it. Just got replacement dash switch 3 days to ship, $25 at Advance Auto. Goes into all gears the way it should, and back to 2wd, no problems at all. Thanks Again!