I am in the process of finding an '05 1500HD or denali. My question: Does a Denali or a 1500HD use signifantly more gas than a regular 1500?

And, How is the Allison tranny for endurance and service?

The Denali does not have an Allison Transmission - didn't come in any 1500 trucks.

Well, I found one and bought it. It is a 1500HD Chevy with a Allison transmission. While driving it home the "Service four wheel Drive" message came on. The dealer near me said it most likely is a sensor on the shifting motor for the transfer case. Anybody have an idea how much it should cost to have it replaced?

It doesn't have an Allison Transmission - whoever told you that was mistaken - crawl under it and see if you see a small spin on oil filter on the transmission - that's there for all Allison Transmissions. You will find there isn't one there. The allison transmission won't fit under the truck without the body lifted 2 inches which isn't done on Denalis. If you find a spin on filter on the transmission please take a photo and post it.

For the service 4 wheel drive message- is the switch on the left of the steering wheel blinking when it gives you the message? If so, probably a bad switch - about $40 dollars and a half hour of work will fix it.

This message has been edited. Last edited by: srode,

Well, I guess you were right. There's no screw-on filter. It is not a Denali, it's just a 1500HD. I thought for sure it was an Allison. Now I'm dissapointed that it isn't. It's a very big tranny, but I guess just a standard one.

No, the light didn't blink. It was just a "service 4 wheel drive" msg. The dealer fixed it and it cost over $300. They had to cut off 4 bolts and replace them when they put the new switch it. ??

Thanks for the info. I will say this, with the 6.0 litre engine it only gets about 15 mpg traveling down the highway and about 11mpg putzing around hauling light stuff and working.

Thanks again, Charley

Ouch $300 for that switch - that hurt - but it's working and thats the good news.

Nothing wrong with the transmission you have even if it's not an Allison - they didn't put Allisons in big block Suburbans either and the trany's hold up fine in that application. Don't flog it, due the right maintenance and it will serve you well. Hope your enjoying the new toy!

Well I finally got back online. Yep I have a friend who has a 2500 diesel and his does have that Allison with the twist off filter. Mine is doing fine. Thanks for the encouragement.

srode... I didn't read Clove to say that it was "$300 for THAT switch"... I read that $300 fixed the problem. And from the need to cut off 4 bolts, it doesn't sound like a dashboard switch was replaced.

It sounds more like the encoder motor sensor was replaced, which is under the vehicle at the lowest part of the transfer case, exposed to road debris, road salts, mud, snow, water spray, and whatever else might corrode a fastener outdoors all the time.

Clove, if you wouldn't mind checking your repair order and posting the part number and description of what the dealer replaced, that would help anyone in the future who, like you, seeks help with the "Service 4WD" message.

While the dash switch was a common fault in earlier (2000-2003) trucks, I've more often read about encoder motor sensor failures in later trucks (2003-2006).

It would be nice to know what exact part was replaced in your truck, to sharpen our list of potential items to look at whenever this error shows up.

Ok, I think I have it. I will go out in the pickup and look for it. The switch was in the transmission. I didn't get the idea that it was exposed to the elements though. I will get the part #.

The part was in fact a "sensor", p/n 88962315. Chevy's price for the sensor was $125 plus 4 bolts and a seal, p/n 12384990. It was supposed to sense whether or not it was in 4 wheel drive or something like that. They found out what the problem was with from the stored code in the computer. Didn't take them long to find the problem with their little magic box. I know an other than GM shop could have done it cheaper, but I didn't have much choice at the time. If I would have known, I could have changed it myself. Do you know how to get to "Motor Guide's" maint. book at the public library? I've been told that is the book that GM uses in their shop.

Thanks for posting the fix Clove - very helpful for others troubleshooting.

Yep. As I suspected and said earlier, you had an encoder motor sensor (88962315) replaced.

The code their black box pulled up was likely "C0327". The fact that this code begins with a "C" is a "clue" that it is a "chassis" code, and unfortunately, a regular OBD-II scanner would NOT have picked up that trouble code.

All OBD-II compliant scanners, by federal mandate, exist to enable all technicians, whether or not employed or trained by an automaker's servicing dealer, can properly diagnose faults with engine and emissions equipment.

This means that you can go to any Auto Zone and rent/borrow a scanner, plug it into the Data Link Connector under your dash, and scan your own truck for codes. But the hundreds of Parameter IDs that you can pull will begin with a "P", for those parameters that are required to assure proper engine function to minimize emissions.

However, auto makers have proprietary leeway when it comes to other systems on the vehicle that do not relate to emissions. Four wheel drive is one such optional system. Since the car doesn't require 4WD to run, faults with the 4WD do not fall within OBD-II protocol requirements, and therefore only expensive scanners containing GM proprietary software (also sold be ACDelco in the aftermarket) can pull a Chassis code.

So you'd need a $2500 Tech II scanner by Techtronix, or the Snap-On 3000 series scanner with the GM upgrades (for about the same price, or higher), in order to pull that C0327 code.

Therefore, even if you had your very own copy of "Motor Guide" service manual (which may not be the best service info anyway), you still may not have been able to diagnose the problem that quickly, or with any precision at all.

So don't kick yourself.

For the future, go to www.helm.com and order the GM Factory service manuals, on paper or on CD, for your year make and model truck.

As for the codes, consider a subscription to OnStar, which has the capability of logging codes for some, but not all, of GM's vehicle systems. It just so happens that OnStar can see a Code C0327 though. That is how I diagnosed mine!

Once the "Service 4WD" message appeared, I called Onstar and asked the lady to read me EVERYTHING she can see on her computer screen, whether it made sense to her or not. She did, and as soon as she stuttered and stumbled through "CO327", even though she had no idea what she was reading meant, I knew right away what the problem was.

As soon as I hung up from her, I called the parts department to the nearest dealer to make sure they had an encoder motor sensor in stock. They did. It's a very common problem. Then I made the appointment with the service department, knowing that I wouldnt have to leave the truck overnight, since they already had the part in stock. I had the truck back 3 hours later, fixed under warranty.

How did I know what the trouble codes meant when she read them? Because I had previously obtained the GM Factory Service manual from Helm, and I read up on all the trouble code possibilities for what Service 4WD could mean, as the message had cropped up before but went away.

When and if you put a value on the the time spent studying ($$$?), and add to that the cost of the Service manuals ($180), plus the $200 a year subsription you still may be dollars ahead with your $300 repair out of pocket.

So again, don't kick yourself.

Enjoy your new ride. I'm sure you'll like the Quadrasteer part.