01 tahoe "Service 4wd" light turning on.

[MAC67]

Hey Guys . Ive been looking around on this problem and its pretty hard to narrow it down , Seems like everyone has differnt symptoms. Its a blizzard outside and a sunday afternoon so im just trying to get ideas.

Wifes truck , she just bought it with 134,000 on it. Runs down the road fine , lights ont he switch all work good. Went to go get grocerys thismorning and i hit the 4 hi " first time ive tried it since we bought it" it went right into 4 high just fine , i made it 2 miles down the road and the service 4wd light came on .
It would not let me shift back into 2hi until i shut the truck off . So i pull off to the side of the road , turn the key off , back on and boom she shifts fine back and fourth 2 hi to 4 hi but when i get to going down the road in 4 hi it will come back on and lock me into 4 hi ,
I can shut the truck off and put it back into 2hi . I know the 4wd is working , No wierd sounds aside from the normal front differential hum.

Any ideas ? could this be the switch even tho it is working ?

[spudz]

find what the code is... its probably got a p0327 in it.

[MAC67]

Originally Posted by spudz

find what the code is... its probably got a p0327 in it.

are you sure it would be code p0327 ? Thats a low voltage code from a knock sensor . Dont see how that can kick out a service 4wd code.

[spudz]

if you find out what the code is let me know and I can walk you threw it

[spudz]

crap sorry got em mixed up.. I meant C0327 either way.. no way to be sure unless you have the codes pulled.. Its either going to be switch in dash, a reprogram, transfer case failure, wireing or transfer case encoder motor. Probably the encoder motor.

[MAC67]

Hey Spudz, i got the code thismorning . i put it in 4 high and drove around the block until it threw the service light on then took it to the shop to pull the code.

It threw a C0305 = Front propshaft speed sensor fault.

any clues ? common thing ? im guessing they are calling the driveshaft the propshaft but i could be wrong

[MAC67]

cant find anything for a "propshaft speed sensor" at any of the part stores.
Called the dealership and they cant either , he did however locate a screw in speed sensor on the transfercase , couldnt tell me if it was it or not. gm part number 12376520
Delco part number 213-347

Would this be the right one ?

[MAC67]

looks like the "21" on the left side right above the front shaft output

[spudz]

NOT COMMON AT ALL!! First make sure the wires arent chaffed anywere. Above the front driveshaft is common for this.

ohm out the front driveshaft speed sensor. should be 1300-2700ohms

if out of range replace sensor.. If its within spec. Get back with me and I will walk you through the rest of the diagnosis. Its number 7 in this pic.

[MAC67]

AWSOME , great diagram . Thanks , ill let you know the results when i get it inthe garage tomorow.

[MAC67]

I knew what the problem was within 3 seconds of sliding the creeper under the truck. the transmission has been replaced with a new one before i we got the truck . Apparently they didnt think to hook up that front speed sensor because the plug was just hanging there. I had a new delco sensor there that i had bought for 25 bucks , i went ahead and put it in because the old one was packed full of mud and ice . no sence in doing it twice for 26 bucks.

Thank you for all the help , it is GREATLY appreciated.

[spudz]

GLAD you fixed it!