ChevyBiH

Hey. I'm worried about my Tahoe.
A few months ago my dad was messing around in the snow. He put the car in 4 wheel drive auto and hit the gas. When he parked, he noticed that it says "service 4 wheel drive" on the dash. We turned of the car and then it went away.

Today I was in my Tahoe and put it in neutral and turn on 4 wheel drive auto and it said service 4 wheel drive again. I also heard like a clank in the back. I put it in 2 wheel and turned the car off and then on and it was fine. When I put it in 4 low or 4 high, I hear the clank but it doesn't tell me i need to service anything.

Does anybody have any ideas on what might be wrong?

mulmur1

Normally, there is an engagement sound when you move from 2wd to 4wd. It may sound like a clunk, but it should not be a whine and grinding sound. There may not be anything wrong with your 4wd and the code may be related to moisture.

There are a number of reasons for the service 4wd error code to be thrown by the computer. It doesn't sound like you are experiencing the 4wd switch to go into different modes by itself, which is good.

It would be a good idea to have the codes read, to see if there is anything wrong. Hopefully all is ok.

Some trucks experience the front transfer case motor encoder ring, needing to be replaced. One of the symptoms is the front transfer case shifting into 4H or 4L without you making the decision.

It would be a good idea to check your differential front fluid level either way.

How many miles do you have on your truck?

ChevyBiH

The odometer reads around 110k miles. Not much for an '03

SabrToothSqrl

Define "hit the gas"

as in gently accelerated or as in floored it for fun?

I hope the first, as the latter would be better suited for '4x4' mode, not auto.

ChevyBiH

He floored it. The car was revving really high.

and by the dash it has the modes that you can put the 4 wheel drive in.
The top says "auto 4x4"

mulmur1

I have never been a big fan of auto 4wd. As SabrToothSqrl noted, when you floor it, 4H would be a better choice. Personally, I don't use auto and select 4H or 4L when necessary. It is normal for auto to clunk when you are being really aggressive with your truck.

SWHouston

HA HA, that's the politest way I've herd yet, to describe something that sounds like a rear end collision !

ChevyBiH

Okay well i went to check the fluid and try to locate where exactly the noise is coming from. I put the car on a lift and put it in neutral and had somebody put it in 4wd. When he did that, the tires started rotating.. Is this suppose to happen or is my car insane?

SWHouston

I don't think that's a problem. I've never run into that before, but I wouldn't be surprised it if was intentional. Given that the Transfer Case has to mesh gears to connect, it wouldn't surprise me if the transmission held a little pressure on a clutch to do that. I doubt if it would be enough to cause forward or reverse movement of your vehicle.

SabrToothSqrl

N on the transmission or N on the transfer case?

4WD Auto locks the transfer case, but not the front hubs. If someone mashed the go pedal, the computer would think the rear wheels were slipping, and then engage the fronts. Doing this while under heavy throttle is a bad idea. You aren't actually in a 'locked' 4WD setup.

This may have caused some damage.

If you want to do that, be sure to use '4 high' and don't do that until you know you are locked in. generally drive for a few feet or more.

You never want to engage any 4 wheel mode while one axle is spinning faster than the other.

There is no center diff (generally) on these SUVs.

as for why it started to move... why was the engine on if it was on a lift?

just leave the key in 'run', without starting the engine.

You trying to get killed? the mass of the tires starting to move / stopping can easily cause a vehicle to fall off of a lift. You vs 5,000 lbs of metal... not a good idea.

Key in run = all accessories will operate. including the 4WD shifting mechanisms.