4X4 light flashes five times will not shift into four wheel drive

94 TRANSAM

MECHANIC
1996 CHEVROLET TAHOE
5.7L
V8
4WD
AUTOMATIC
308,000 MILES

I had the truck in 4H, needed more torque so I hit the 4L button and all was well. Got unstuck in the snow and hit the 2H button and it went right into 2H. A few miles down the road I hit some more snow so I went to hit the 4H button again and both the 4H and 4L buttons flashed five times and went back to 2H. Now it doesn't matter which button I hit (4H or 4L) both lights flash five times and go out. No shift noise at all and intermittently all the buttons go dead, no lights for a few minutes like an auto reset breaker pops and it takes a few to reset.

I am familiar with this system and have fixed many but I have never seen both lights flash at once.

Anyone heard of this?

7 Replies

KEN L

MASTER CERTIFIED MECHANIC
48,363 POSTS

Hello,

Yes this happens when the encoder goes on on the transfer case. Here are diagrams to help you change the unit out. #73 is what you need to replace. Check out the diagrams (below). Please let us know what happens.

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Tuesday, February 26th, 2019 AT 11:26 AM

94 TRANSAM

MECHANIC
680 POSTS

Hi Ken, Thanks for the reply. So the back story is I plowed through a four foot snowbank into a driveway when I did the truck kicked to the right and the rear tire slid into a ditch with five feet of snow in it. The relevance here is the whole drive train was hot and all that snow packed tight under the truck in every single nook. Even all the way up over the transmission. With it all being hot the snow melted enough to soak the rest of the snow which in turn quickly froze solid.
So I got under there yesterday to check for ripped wires etc and found a solid block of ice from the rear of the oil pan back to the start of the driveshaft. Couldn't see the transmission, front drive shaft or transfer case at all. So chiseling away and melting with map gas I got to the front drive shaft which wouldn't turn at all. Long story long I got all the ice out and it shifted right in to 4H and 4L right away. I'm not sure what exactly was wrong except maybe the front shaft has to be able to turn a bit to align the transfer gears. Or maybe the encoder was mad at me and said no way I don't know but it is one for the books. Thank you have a good one.

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Tuesday, February 26th, 2019 AT 8:19 PM

KEN L

MASTER CERTIFIED MECHANIC
48,363 POSTS

That.S a good one I think you were right about the encoder. Use 2CarPros anytime, we are here to help. Please tell a friend.

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Wednesday, February 27th, 2019 AT 10:42 AM

JNIENHAUS1

MEMBER
1 POST
1999 CHEVROLET TAHOE

1999 Chevy Tahoe

I have a 1999 Tahoe, with dash push button 2H, auto, 4H and 4L buttons. The check 4wd light came on a couple weeks ago and the tech checked the code and said it was a switch problem. I took a 100 mi trip yesterday and after stopping to unload it had shifted to 4L and stayed there. The dash switch was replaced and now their telling me the tranfer case decoder is bad< $800.00. I cannot find this part or any info online any where. Tell me all you know

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Wednesday, February 27th, 2019 AT 10:42 AM (Merged)

RHALL77