Hello all, need help. Just bought a 2001 blazer. 143000 miles in really nice shape. The 4wd worked fine the first 2 weeks. Went in and had radiator flush and fill, transmission flush and fill and had them change transfer case fluid while they were at it. Tranny fluid level is good. A week ago my service 4wd light came on and then went away. It does this here and there now. The problem is it won't go into 4wd. The 2hi button is lit up but won't go in 4 hi, 4 low or 4auto mode. It just stays on 2hi. I hear no clicking sounds or anything when I hit the other buttons. Is this just a bad switch?? Where should I start troubleshooting? When I start the truck and all the dash lights come on all of the lights for the 4wd buttons come on then go off like they should and the 2hi stays lit. Thanks in advance!!!

 

You can change switch easy fix also check under battery the vacumn line to the transfer case is under there they might have pulled it loose working on the radiatorThats what happened to mine just plugged it back in I did put new line in Worked fine

 

I'm having the same problem but mine when all the lights come on it shifts fine but when the 2wd light is on it won't shift it slips what are the punch button 4wd called need to order one

 

Also check for corrosion on the TCCM connections , this is also a fairly common issue with these trucks......If you can get the code read with a scanner capable of reading them, it may help in trouble shooting if the switch isn't the issue.

 

What's the Tccm I just replaced the box on the passage side on the floor noticed the when I put it in4wd the service light comes on

 

TCCM is that box that you replaced. Did you replace with the correct new one?

The 4WD controls are pretty trouble free. Lights in the buttons are driven by the TCCM, so their on/off status says nothing about the push button switches. Encoder motors on the transfer case are much more likely to go bad.

Start by reading the diagnositic codes. 3-button controls you use a jumper. 4-button Auto 4wd - you must use a capable scanner.

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