2000 Silverado Auto 4wd function

[boomersbandits]

If I put my truck into the Auto 4wd mode (top circular switch on left dash) the truck locks into 4wd. I have replaced the switch and still have the same problem. I understand that this mode allows for a sensor to detect speed differences between front and rear axel to determine when traction needs to be applied to front tires. No codes are present and therefore the encoder sensor is not at fault since the truck functions correctly in 2-Hi, 4-Hi, and 4-Lo. But the truck is constantly engaged when in 4wd Auto which it has never done before. Any ideas?

[Sonny01]

I have a 2000 also and when I hit the 4WD AUTO switch I can feel and hear a difference when I go around a corner. It doesn't even have to be a tight corner. Maybe mine has a problem too! But mine has been like that from day one. I did take the switch apart once and resolder the bad connections that were cracked. That was because I couldn't get anything but 2WD to engage. Maybe someone with more knowledge can help us out here.

[ColoradoSilverado]

Seems like I'm having the same problem always thought it was normal but it definitely makes noise when turning on dry pavement.



Bert

[boomersbandits]

Well gents this is what I have found so far in talking with my former associates up in Washington.

Both the switch and encoder sensor will set codes but there can still be an internal problem (which won't set a code) in regards to the clutch in the transfer case. My truck has 91K (purchased with 76K) on it and I know that regretably I was ignorant and ran the truck in Auto 4wd for the 15K I have owned it. The dealer I purchased it from stated the previous owner also ran it constantly in that mode also and furthermore the service manual states that running it in this mode with only slightly deminish the full economy as opposed to running it in 2wd mode. However, this is not entirely true.

When running the truck in Auto 4wd power is applied to the front axel (thus causing a noticable fuel difference) but the transfer case clutch only engages and therefore applies traction to the front tires only when a speed differential between the rear axel and front axel is notice i.e. if you lay on the throttle and slip the rear tires or hit snow/slush/ice. Then the encoder sensor sees a speed difference between rear axel and front axel at it causes the clutch to engage and locks the front axel up adding the needed traction to the front tires.

Over time the clutch in the transfer case can begin to stick or worse cause can even lock-up due to wear and tear. But there is some good news.

1) You can flush the transfer case fluid. Either get the synthetic fluid that was originally in the truck (find this by searching with your VIN) or use whatever Chevrolet has now deemed a better transfer case fluid (dealer will know this). When you do flush the transfer case attempt to catch some the fluid in a glass jar or smear some of the excess on white paper. Most likely this fluid will be blacker than coal in snow, but also check for any debris which would point to bullet 2. Once you have flushed the fluid the clutch will again be lubricated and you should cycle the truck through all modes (Auto 4wd, 2wd, 4Hi, and 4Lo) to help continue lubrication through engaging and disengaging the clutch. A second flushing may be needed depending on a multitude of variants such as mileage and if the transfer case fluid has ever been changed.

2) If debris is found in the fluid sample the clutch may have suffered grinding and therefore isn't engaging (the case if you can't get it out of 4wd modes or out of 2wd mode) or locked/sticking. In this case the clutch will have to be replaced. It appears that if this is in fact the symptom on my truck that my warranty will cover it.

My truck has never had the transfer case flushed, not when I owned or when the previous owner owned (you can check this by getting a VIN report from a dealer). The only thing ever done on it was replacement of the rear transfer case seal.

Hope this helps so far. My truck is currently in the shop going through the bullet 1 process. I will keep you posted on the outcome.

[JDCowboy]

I believe that Boomer has told you the answer. I have a 2001 with a similar problem. My front diff was busted when I bought it. Thru many tears a little cussing and some great thinking I replaced the front diff. In the process I discovered that the front drive shaft never releases to spin free even when the truck is in 2wd mode. I suspect that if you check your truck you will find that yours does the same. Your front drive shaft is always locked in. This may be a way to troubleshoot. I was not aware of the possibility of flushing the fliud being a cure. I am going to go home and try that on my truck to see if that cures it. Good Luck......

[Sonny01]

Just remember to replace the transfer case fluid with Auto Trac II that you get from the dealer. I had the dreaded clunk, flushed out the transfer case and put in Auto Trac II and the clunk was gone.

[JDCowboy]

Originally Posted by boomersbandits

If I put my truck into the Auto 4wd mode (top circular switch on left dash) the truck locks into 4wd. I have replaced the switch and still have the same problem. I understand that this mode allows for a sensor to detect speed differences between front and rear axel to determine when traction needs to be applied to front tires. No codes are present and therefore the encoder sensor is not at fault since the truck functions correctly in 2-Hi, 4-Hi, and 4-Lo. But the truck is constantly engaged when in 4wd Auto which it has never done before. Any ideas?

Hey Boomer,
Did this proceedure fix your truck. My xfercase appears stuck in 4whl drive. It never releases the front drive shaft to turn free even in 2wd mode. I am doubtful that the flush will free that up. I have gotten 2 from a wrecking yard and they appear to have the same problem. There does not seem to be a 2wd mode. very strange....Need any advise I can get I am stumped and I cant seem to find a mechanic that knows anything about it including the dealer.

[BusterD62]

I have an 07 Suburban with 31K miles, same issue with Auto-4WD light.

Must plead ignorance on using 2WD as preferred mode of operation. I was told when I bought it at dealer that Auto position Switched between 2WD and 4WD.

I have put all these miles on with switch in Auto. I will have the xfer case fluid changed at dealer and have them check for debris. Thanks for the tip, the dealer was stumped!!

Also, I had to have a rear main seal replaced this past week. this seems quite unusual for a car with 31K miles and a year old. Any experience with root cause of this failure.

[kahjdh]

shouldn't the solenoid on the front axle disengage the passenger drive axle when you go into 2hi?

I never liked the auto switch b/c I couldn't control the shifts, always figured it would lead to the front end grenadeing.

[silveradofirerescu]

Shouldnt you be able to jack the front end up and spin the front tires in gear and 2hi?

[semisendiz]

My "auto" button will not engage. I have been running my truck on 2HI for most of the time. It does switch back and forth from 2HI to 4LO and/or 4HI, but the "AUTO" button feature does not engage. I replaced the switch with no luck. The first time I tried to engage, the message center said to check my transfer case with the the dealer. Anybody knows why, besides the obvious answer?