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Hello,

I've read many of the Service 4wd threads. I think I understand how the 4wd system works.

My 2004 Suburban had the Service 4WD message today (it has a couple times in the past year since we've bought it) and none of the indicator lights in the pushbutton 4wd switch on the dash were lit up. Pressing switches didn't appear to do anything. It was in 2wd mode. It's snowing today and my wife was going to take it to work. She took our other vehicle. In case it matters, the 4wd selector switch yellow indicator lights work, but the white "dash" lights in it don't work.

I went out later and the 4wd system worked fine. When starting the Suburban, all the indicator lights were lit on the 4wd switch until it just showed the 2wd. I pressed each of the buttons and it went into all 4wd modes. This tells me that the fuses, switches, transfer case motor is good. Must it be an intermittently bad ground under the driver's door then? It can't be a fuse.

I'm hoping I can get right to the exact fix instead of laying on the snow-covered ground for hours trying to find and/or fix something that I'm not sure will be the actual solution.

Thanks for any advice.
 

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I use AUTO most all winter here in Michigan. I had a new 2004 Sierra SLT and I had 4wd switch and encoder motor in transfer case) issues under warranty so these model years had problems with these electronic parts. I recall going back 2x before the found the culprit, some electronic control. Consider having the GM dealer trouble shoot it. Replacing some of those parts willy-nilly can be costly and you may waste money and time replacing the wrong parts...There was also some issue with the transfer case fluid and they came out with a better version for use in cold climates. Have you even replaced the transfer case fluid??
 

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"service" messages will have an OBD2 code connected to them, cheap code readers can not read these codes, go to a parts store and have them read the codes.
 

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2001 Suburban 5.3L, 307k miles
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4wd in Auto basically just means it's mostly running the transfer case clutches mostly rear wheel drive (2wd) and slightly engaged front wheel drive.
When wheel slip is detected, it fully engages the front wheel drive to get 4wd in slippery road conditions.

I don't use Auto 4wd as it frequently modulates the transfer case clutches and they can get worn sooner than when just engaging 4Hi .
 

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Fwiw, GM explanation

AUTOMATIC TRANSFER CASES
The last category is a combination of 4WD and On Demand AWD. These transfer cases have a 2HI, Auto-4WD, 4HI, 4LO and Neutral position and would fall in the general 4WD category. This transfer case has the operating characteristics of both an On Demand AWD and a Part-Time 4WD system depending on the mode selected. If the transfer case is operated in 4HI or 4LO, it will behave as a Part-Time 4WD system. If it is operated in the Auto 4WD mode, it will behave like an on-demand AWD system.
This transfer case uses a clutch pack to allow for a difference in speed between the front and rear axles in the Auto-4WD mode. In the 4HI or 4LO modes, there is no allowance for the difference in speed between the front and rear axles. An example of a vehicle with this would be a Sierra with a push-button transfer case with a 2HI, Auto-4WD, 4HI, 4LO, and Neutral positions.
 

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The other part that gets activated in 4 Auto is the passenger side front axle actuator.
When in any of the 4wd position, including 4 Auto, the right front axle halves are connected together.
No big deal; but remember in a turn, the 4 wheels all turn in different turning circles.
And when the front right axle halves are engaged, one of the front wheels is required to turn at the same speed as one of the rear wheels.
If it does turn at the same speed, a tire will be subject to slippage and subject to wear.
If it does not turn at the same speed, the transfer case is subject to clutch slippage.
 

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Sometimes the 4wd might not engage if pressing buttons while sitting parked. Try moving by putting it in drive while pushing the buttons. The shift might be blocked and moving the vehicle slightly will allow gears to mesh.
 

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2003 Suburban 4x4 203000 - If I have 1-2 feet of snow to go through after a while it says service 4x4. Then goes away. Been happening for years except we have not had alot of snow lately. No 4x4 issues.
 

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2005 Silverado 1500 4x4
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Most likely the ground under driver door. When my "Service 4WD" light comes on I crawl under and clean the ground connection thoroughly. Has worked every time. I live in a snowy area so it's easy for the connection to get corroded with all the crap they put on the roads.
 
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