The main problem here is sometimes the 4wd switch will light up with no service 4wd light and sometimes it will not light up with a service 4wd light. Ihave 2TCCMs.TheoriginalTCCM when in I get no lights at all on the 4wd switch with a Motor A/B circuit code. The junkyard TCCM will make the switch light up attimes and sometime set a B2725Active transfercase switch malfunction code.When the switch will light it will not go out of 2wd hi and I will push 4wd hi and 4 lo will blink and thats all. I have use of a tech 2 and a GM flow chart so I went to work. Theoriginal TCCMin the vehicle has a motor A/B circuit code and I cannot use the tech 2 to manually put it in all 4wd positions. With the junkyard TCCM i can command the 4wd postions and i can hear underneath the vehicle what sound like axels engaging and i can hear the encoder. The problem is even tho I command it in 4wd and hear it engage it isnt physically in 4wd. The code that pops up every few key cycles isa active transfer case switch malfuntion. So i grabbed my flow chart and tested the 8v reg circuit. With the junkyard TCCM i am gettin 6.75 volts and thats out of spec. I also tested resistance for all the 4wd functions and they were also all out of spec. I then plugged in the original module which has the motor a/b code in it and got 8.1 volts which was in spec but the resistance was also out of spec on all modes. When i first had the problem I bought a new switch just praying it fixed it and it didnt so I then returned the new switch back to my dealership. I havent pluggeda new switch in with the junkyard module yet tho. I am leaning towards throwing an encoder motor in it. Sorry for the long post. Any help would be appreciated.

 

Well it sounds to me that you have gotten another bad module. With the problem GM has with these modules I never buy them used, I always spend the little extra and get a new one. Most likely that will cure your problems, just if you want to make 100% sure go through the flow charts again, and make sure you get the same test results. Good luck.

 

I put the new encoder motor in and get the same problem. I guess im gonna have to go and buy the new module and pray thats it because I have gone through everything else.

 

So I bought the brand new module and now all the ranges on the switch work but everything but 2 hi blinks when I select them. So I went looking under the hood and finally found the problem. The vaccum line was loose that goes on the vacuum ball in the L/S fender. Hooked it up and everything works. Thanks for the help I ended up needing a module and a new switch on the dash as well.