2003 Tahoe 4wd issues

[pjw67]

Recently bought a used 2003 Tahoe - 4x4 worked intermittantly. Bought on the cheap. Seller had quote from dealer to fix 4x4 for around 1100(reflash tccm and replace encoder). Service 4wd message was always on the dash. Dealer said code was C03-27 i believe. Truck was always stuck in 2wd high. Lights worked on the switch - nothing happened. Everyonce in a while you could shift it into 4x4 hight or auto modes. I would usually take a couple tries to then switch back to 2wd.

I had local dealer reflash the tccm but couldnt afford the remaining 900 for the new motor and labor. I purchased the new motor and installed it myself.

Still in 2wd high and nothing happens when you hit the buttons. I have read all the forumns about the switches being bad - so I switched it out with another good one from a friends truck. No change. My switch worked in his truck.

What else is there to look for? Tccm is good. New encoder motor, good switch. I cleaned up the grounds under the drivers door and inspected as much wiring as I could find for breaks.

Any ideas where to go next?

 

[S7A2G6]

You are not alone. I too have a 2003 Yukon SLT. I started with the actual push button on the dash. No avail. Replaced the "computer" behind the headlight switch. No avail. Just today, tried to install a brand new encoder motor. No avail. The truck actually does better with the old motor in it. I have been pulling my hair out over this since 100,000 miles. I am now at 287,000, so needless to say I am bald now...

 

[pjw67]

I finally broke down and took it to an auto electrical diagnostic shop today. After a couple hours they said the tccm was shot. The same TCCM that I just paid a local Chevy dealer to reflash last week. The diagnostic shop quoted a large sum to put a new gm tccm in and program it. I asked if they would put a used one in - they said they couldnt. I paid them for the diagnosis and picked up a used TCCM from the junkyard on the way home. Snapped it in less than 5min and the 4x4 works every time now. I assume the new tccm from gm needs to be flashed and the junkyard one doesnt. Who knows - but it works now.