Intermittent 4wd Light On When In 2wd

bandera · December 23, 2009

I have a 2000 Silverado Z-71, 107000 miles, 5.3, automatic transmission, with MANUAL SHIFTING TRANSFER CASE. A few days ago, while driving in 2WD, the 4WD light came on. Thinking I might have bumped the shifter, I looked and it showed to be in 2WD. I shifted it to 4WD and felt the four wheel drive system engage. I could tell it was working correctly by the feel and the harder turning (on dry pavement). I then shifted it back to 2WD and the light cleared but came back on after a minute or so and I could hear a slight grinding noise coming from the driver side front wheel area. I then shifted it back to 4WD and the noise immediately stopped and could feel the 4WD system working. Then put it back in 2WD and the light cleared and then came back on after a few minutes. This time no noise from front end. This has happened several times a day. Some times with the noise, some times without - BUT in every case the truck is in 2WD and the 4WD light comes on. YESTERDAY I drove it all day in 2WD and the 4WD light did not come on at all nor did I have the grinding noise problem. Today the problem is back. To me it seems to act like its trying to engage the front axle while the transfer case in still in 2WD. When I put it in 4WD everything seems to be working right. But I don't want to be driving around on dry pavement in 4WD. I have tried it in 4WD LO and everything works fine. Tried backing it up in HI & LO with no problems. Right now it is in 2WD with the 4WD light ON and NO NOISE from the front end area. As long as it stays like that I guess I'm ok until I can figure out what the problem is. But as soon as it starts making that noise I will put it in 4WD, BUT I don't want to be driving around in 4WD on dry pavement when I don't need it. Anybody have any ideas what the problem and fix might be ?

alwcurlz · December 23, 2009

Sounds like the selector switch in the floor control is moving when it should be anchored in place. I'd take the cover off that is around that lever and check things out. May be just a loose selector switch.

gmtech4 · December 24, 2009

the switch is in the t-case and no where near the lever ,could be the switch but don't throw parts at it,or do what ever you want

alwcurlz · December 24, 2009

the switch is in the t-case and no where near the lever ,could be the switch but don't throw parts at it,or do what ever you want

So the lever isn't connected to the transfer case? Do you have an illustration where this switch is?

bandera · December 25, 2009

the switch is in the t-case and no where near the lever ,could be the switch but don't throw parts at it,or do what ever you want

So the lever isn't connected to the transfer case? Do you have an illustration where this switch is?

Are you saying the switch is mounted INTERNALLY in the transfer case ? Are there any schematics or service manual information on this ?

gmtech4 · December 25, 2009

i realized later that I said it wrong,

the lever connects to a plate inside the t case,the switch threads into the t case ,it has a ball on the end of it that rides on this plate and in 4wd the plate pushes on the switch and energizes the donkey dink on the frt diff and 4wd is born .(manual system only)

merry xmas

bandera · December 27, 2009

i realized later that I said it wrong,

the lever connects to a plate inside the t case,the switch threads into the t case ,it has a ball on the end of it that rides on this plate and in 4wd the plate pushes on the switch and energizes the donkey dink on the frt diff and 4wd is born .(manual system only)

merry xmas

Very good !!!!! Now we are getting somewhere. Ok, now how do I get to that "donkey" ?

gmtech4 · December 27, 2009

the donkey dink is the frt diff actuator,power goes thru the switch and the donkey dink locks the frt diff,

to check it ,remove the actuator ,pull shifter back,turn key to the run position and the actuator should go out and dash lt turns on,or

unplug the switch and check for power

get a schematic ,you'll see how it works

alwcurlz · December 27, 2009

gmtech4 · December 27, 2009

whats your question Adam?

bandera · December 31, 2009

Can I get to the internal switch in the transfer case from the outside, or does the transfer case have to be removed from the truck to get to it ? It went two days without a problem then did it again. After that day, it has been three days since it has happened. Now I know it didn't fix it's self, but cant figure out why it is so erratic. Guess I'll see how long it will go this time before it acts up again.

Is there anywhere on line that I can go to look at schematics and drawings of this ?

bandera · January 8, 2010

Can I get to the internal switch in the transfer case from the outside, or does the transfer case have to be removed from the truck to get to it ? It went two days without a problem then did it again. After that day, it has been three days since it has happened. Now I know it didn't fix it's self, but cant figure out why it is so erratic. Guess I'll see how long it will go this time before it acts up again.

Is there anywhere on line that I can go to look at schematics and drawings of this ?

Still have not gotten this fixed yet. It goes for a day or two without any problem , then comes up again for a day or two. Went by Auto Zone and put it on their scanner. It shows a code P1875.

Is there a website I can go to to see the exploded view of this to see where the switch is located ?

bandera · January 16, 2010

Does any of this system work on a vacuum ? I've noticed that when the light has cleared, that if I "get on it" like passing a car, going up a hill, or quick acceleration that the light will come on.

Nytemare · January 16, 2010

Does any of this system work on a vacuum ? I've noticed that when the light has cleared, that if I "get on it" like passing a car, going up a hill, or quick acceleration that the light will come on.

Sounds like something is loose. when you "get on it" the drive train torques and makes contact...so broken wire or loose connector would be what I would look for.