Intermittent SERVICE 4WD Message

[Michigan]

2004 Tahoe z71 4wd with 4auto, 2hi, 4hi, 4lo

I’ve had this truck for about a month now and have not had any issues with the 4wd system when I’ve tested it.

When testing I mean switching buttons from 2hi to 4hi and listening for the actuator to make the noise and engage. Im not an expert in other words. So when putting it to the test my way, it’s engaged fine and 4wd seams to work fine. Have not had any snow so haven’t had to use it yet.

I should note that the other day we had some heavy rain and I put it in 4auto in my drive back from work which was about 30 miles. No problems there and that night I also get back into my later that night and drive a few miles.

This morning I get into my truck and it was left in 4auto so I switch it back to 2 hi as it’s dry out and I drive it to work 30 miles no issues. 6 hours later get back into the truck to drive home and no issues.

After that drive about an hour and a half I get back into the truck and turn the key and no lights at all in the 4wd switch and the service 4wd message appears on the dic. I’m like wth, hit the button on the switch and nothing happens. Turn the truck off and back on and same thing happens. Then do the same and drive it around the block and come back and turn off and on and same thing happens so I decide to take a different vehichle.

Just got back home now about 5 hours later and decide let me go out to the truck and see what happens. Turn the key and the light comes on the switch and goes to 2hi where it left off and no message on the dic as if nothing ever happened. I hit the switch to 4hi and hear it actuate and turn over smoothly and then hit back to 2hi and switches fine. Idk

Like I said the truck is fairly new to me and I had to replace the battery after a few days of owning it. Not sure if that is relevant or not. I was reading about switch going bad which I was aware of before and tccm, atc fuse but with all his happening and fixing itself I’m asking if it’s an indicator of a problem soon to come?

 

[zraffz]

I bet it's the 4wd control switch on the dash. My wife's truck had the same issue. Be careful, it can get stuck in any combination of those settings!

Only other known issue with these autotrac transfer cases is they do occasionally have an issue where the internals rub a hole through the magnesium casing but that isn't the issue.

 

[swathdiver]

Could be the BCM about to go bad too. Get a Tech2 so you can properly diagnose your truck.

 

[Michigan]

Thanks for the replies.i had no other issues this morning to and from work so not sure what was going on.

When a switch goes bad in these trucks does it make the service 4wd go on in the dic?

 

[zraffz]

Yes... It's a common issue for these trucks with the autotrac to have an issue with the circuit board.

Buy it from a parts store with a long return duration and test it out for a few days lol

 

[Chubbs]

There are a number of different things that will cause a 'service 4WD' fault. The dealer had to replace the encoder ring on mine because the 4WD wasn't lit up & didn't change modes when I took the truck for a test drive. From my research, the encoder sensor is most common fault. Next is the switch bank. Then you have the module & front axle actuator not immune to failure. The easiest to diagnose is the module (brain) because diagnostic equip (aka TECH2) will not connect to it; sometimes the dealer can fix it with a reflash/update. There is a YouTube video by 'MAY03LT' where he instructs the DIY testing of the switch bank. If you want to DIY without spending $1,000 on the hardware capable of reading the body modules, start off by manually testing the mode switches with a voltage meter; if that checks out then throw $50 or whatever it is @ the encoder ring. You will find videos on the replacement. Most people aren't going to have the software (or the extra $$ to purchase it) required for diagnosing the transfer case.

I got a random 'Svc 4WD' last month after driving in some flooded conditions. After a few days I narrowed it down to the transfer case connector harness underneath the truck. Water got in there and nothing worked so you might unplug that to make sure the pins are clean & dry.

Make sure to drain & refill the trans case using the AutoTrak2 lube, ONLY (use plumbers tape on the bolts/fill-plugs or buy a brand new set) It can be purchased from the GM service dept, NAPA auto parts, eBay or Amazon. You need 2 Liters/Quarts. Drain & refill the front diff with 80w conventional. The rear is 75w-90 synthetic. Drain & refill the transmission with Delco Dex6 synthetic. Replace the fuel filter while you are already working under the truck. VIN 'z' as the 8th digit (flexfuel) has the serviceable fuel filter. Sooner the better as the fuel pump is known to fail. Better to spend the $$ on preventative maintenance versus all-out hard parts R&R.

Give the transfer case rearmost output housing a good inspection once a month to catch a pump rub issue before it gets out of hand.

 

[Fless]

I have essentially the same truck as the OP, and had similar issues at about 92K on the clock (not long after I bought it). I'd be driving along and the light on the dash switch would show "neutral", but I'm cruising along with power so I know it's not in neutral. Stop, turn off engine, restart, the light switches back to 2wd and everything is normal. Ended up being the encoder motor on the transfer case. Not really all that difficult to change out. Oh, and we did get the Service 4WD message intermittently.

Not much later we noticed that in 4x4 there was no power to the front wheels, had an audible clunk when switching drive modes, and had to have the T/C rebuilt. FWIW, and not sure if true, I've have heard that a T/C on its way out can take out the encoder motor.

 

[swathdiver]

The easiest to diagnose is the module (brain) because diagnostic equip (aka TECH2) will not connect to it; sometimes the dealer can fix it with a reflash/update.

Great information Joe. On the GMT900, the Tech2 can see and control just about everything related to the TCCM and 4WD. Actually, I think it can and control everything related to the TCCM and 4WD. I figured the GMT800s to be nearly the same.

Tech2s can be had these days for $275-400 depending on options. They were replaced in the 2014 model year with a newer system but can still service early 1990s through 2013 vehicles and flash/reprogram modules if needed with Tis2Web.

 

[Chubbs]

the only 1 that I saw under $1k was via that link you posted a while back. They are the business though; I watched a YouTube video that a tech posted diagnosing 4WD faults.

 

[Doubeleive]

I would start with the dash switch first, there not costly and easy to replace, I had to do mine and it resolved the problem (its the most common issue), junk yards have them sometimes, if it turns out to be the encoder motor they run about a buck and half last time I checked and its easy to do as well, there is a separate issue of wheel sensors (abs) but unless your getting brake feedback at the end of a complete stop or a abs light on then that's probably not a issue but they can be related.