Well I traded in my 2003 5.3L 1500 Silverado on May 1st. Before I traded it in I checked the speedometer with my GPS to give me a point of reference before I tried to check my new ride. The speedo read 75 and the GPS read 74.3, that seems to be within reason.


Well I picked up my new 2004 2500HD CC Duramax/Ally, which I had the dealer swap out the stock 245's for 265 Revo's (might I add the best looking tires I have seen and the best traction so far!). The salesman volunteered to have the ECM re-flashed for me for the tire size. So I brought along the GPS to check it on the way home, well sure enough its off the 3.9% for the tire size difference. Well it went back to the stealer yesterday for them to check it and try it again. I was told that it was loaded with the latest software from GM and the tire size was updated. Last night I check it with the GPS again and still no difference, nothing has changed! Still off by 3.9%!!


So what's the truth behind this? Is GM not allowing the tech's to perform the update? Or is the tech screwing something up? Is there anyone in the Minneapolis area that has experience changing these settings?


I guess if someone tells me its not gonna get fixed then I am willing to adjust and live with it, but I would prefer to have the mileage, speedo and DIC correct, the extra mileage on warranty is nothing in terms of my yearly driving habits so I am not concerned about that.


Thanks


Edited by: Grabs

I watched a tech try to reprogram mine with the tech 2. He went through the whole process, and when he told it to recalibrate, the tech 2 said unable to calibrate at this time, so whatever that means.

GM Dealers at this point in time cannot recalibrate the speedo on a Duramax. What they can do is recalibrate the ABS brake controller which has nothing to do with the speedo or DIC.

Why can't this be done? Or can it be done and they (Corp GM)aren't allowing it to be?


Is this a warranty related item? My dealer did the tire swap for me, this was all done prior to taking delivery on my new truck, so what is the rational behind not allowing them to be updated?

Why can't this be done? Or can it be done and they (Corp GM)aren't allowing it to be?


Is this a warranty related item? My dealer did the tire swap for me, this was all done prior to taking delivery on my new truck, so what is the rational behind not allowing them to be updated?





Can you say "Lawyer"?


All these vehicles are designed, tested, and certified in certain configurations. If you change something and the vehicle is involved in some sort of accident where lawyers get involved, the manufacturer usually gets sued.


So if GM will not sanction any changes you made, they are pretty much off the hook.


What really is irritating about their position, is that the larger tires come on the 3500 SRW. So, in short they (GM) could easily do it but choose not to...http://www.dieselplace.com/forum/smileys/Disapprove.gif


Now as I understand it, the Tech II reads the serial number of the vehicle and coordinates that information with GM's computers, so if there's something that's not approved for that particular VIN, the dealer can't do much about it.


Or at least that's my understanding of it...http://www.dieselplace.com/forum/smileys/Ermm.gif

So in theory, could my 2500HD be programmed with 3500 software and then be accurate? Or will the VIN prohibit a 2500HD to have 3500 software?


And what about the legality behind an inaccurate speedometer and odometer fraud?Edited by: Grabs

Yes, yes, and you changed the tire size, any problems associated with that are your problem...http://www.dieselplace.com/forum/smileys/Confused.gif


Some dealers will refuse to diagnose any problems with the truck if it has the wrong size tires and or wheels on it per GM. It's mostly a dealer thing on that, but the official position of the factory is that you changed it so it's not the factory's problem.


That ain't right per Mangusson Moss, but that's life. Don't like it? You can try another dealer, get your own lawyer or put the factory size stuff back on it.


This changing the size of the tires thing comes up time and time again. GM isn't going to change their internal policies because you and a number of other people want bigger tires...http://www.dieselplace.com/forum/smileys/Disapprove.gif


Sorry to be so discouraging, but that's kinda the way it is.


As far as your dealer installing the tires, well he's an independant business man/woman with a franchise, not the factory.

"As far as your dealer installing the tires, well he's an independant business man/woman with a franchise, not the factory."


- Yeah, but that sales person allowed the change to be made even before Grabs took delivery of the vehicle, and also volunteered to have it flashed... In legalize i would assume that that sales individual is now responsible if they had not mentioned it voiding any warranty. Now if there is no problems, which im not sure there will be with that type of change, then great, but what if ?? Then what ?? Is the sales person who made that deal responsible ?

Kind of answered your own question didn't you?


Look, as I said above, it isn't right but you can always get your own lawyer. GM's got lots of them...

Sooooooooooo, will the DIC and speedo be correct or not if they are able to get tech 2 to change it??

A programmer will be out soon enough I am sure that will be able to recalibrate everything from lawn mower tires to 40 in. boggers. If gm is that retarded to void anything changing 245's up to 265's that is pure bul@@@t. End of story.

Following is the text of a Bulletin sent to dealers a few days back.

-----------

Info - Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns #01-03-10-010C - (04/20/2004)

Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns

2001-2004 Chevrolet Silverado Pickup Models

2001-2004 GMC Sierra Pickup Models

with Allison® Automatic Transmission

This bulletin is being revised to add the 2004 model year and additional vehicle/tire sizes. Please discard Corporate Bulletin Number 01-03-10-010B (Section 03 - Suspension).

Proper diagnosis of engine, transmission, speedometer and cruise control concerns must begin with an inspection of tire/wheel size.
• The 2500 series trucks have LT245/75R16E tires as standard equipment.
• The 3500 series trucks with dual rear wheels have LT215/85R16D tires as standard equipment.
• The 3500 series trucks with single rear wheels have LT265/75R16E tires as standard equipment.

A truck that has different tires and wheels will have engine power/performance concerns, transmission shift concerns, speedometer registered speed concerns and cruise control concerns.

Before any diagnosis is performed for these types of concerns, inspect the tires/wheels for the proper tire and wheel combinations.

If a truck is found to have other than the above listed tire sizes, no further diagnosis should be undertaken until the original size tires and wheels are reinstalled on the truck.

The Engine Control Unit (ECM) and Transmission Control Module (TCM) use (RPM) and (VSS) inputs as operational parameters for engine torque, transmission shifting, cruise control operation and speedometer indicated vehicle speed.

Calibrations for different tire/wheel combinations are not available.

Therefore, changing of tire and/or wheel size should not be undertaken by dealerships or truck owners

Reinstalling the proper wheels and tires on the vehicle, prior to performing any type of diagnosis of the truck, would be considered truck owner responsibility and not a warranty repair.

There should be an easy fix to all these problems:
- buy the truck with the standard tire / wheel combo
- buy a truespeed for approx. 170 $ and your favorite new tire / wheel combo but keep your original tires/wheels
- install truespeed with new tires/wheels
- mount original standard tires/wheels when going to GM for service
- the truespeed has a flip switch for your original and new tire/wheel combo to select

so let me get this straight, you can get a 1 ton with 265's but not a 2500? And the allision knows the difference? I call bu@@@@#t again. That service bulletin is crap, sorry just the way it is. If gm gives me a problem over stuff like this they will wish they hadn't.

I got the same runaround at my dealership in Encinitas, CA last week. Maybe they were telling me the truth?





GarEdited by: biggar

okay currently GM is re thinking there position on tire size cailbration for trucks, primarilly 20" calibrations. depending on the truck 275/55/R20 calibrations are avail, but for gassers only. GM HAS NOT CHANGED their position on the Duramax, say you have 265/75/R16 tires, they will only let you change to a 265/70/R16 calibration. It is a liability factor to prevent roll overs. You can't blame them.... when WE THE PEOPLE sitting on the jury's giving judgements for spilling coffee in your own lap. WE THE PEOPLE are the ones to blame for the tight restrictions, and untill WE THE PEOPLE start taking responicbility for our own actions.....no matter how stupid they might be, it will never change........

So, anyone have a list of Valid oem sizes for the 04 Duramax in the 2500, is it only the 245's and 265's?


Just took delivery of my LLY ext cab 2500HD Sat. Those 245's look awfull small in those well's


Yes, my first post here..


02B12S - my other ride,2002 1200S Suzuki Bandit


JJ

2500HD's come with 245's, only the 3500SRW's come with 265's.

okay currently GM is re thinking there position on tire size cailbration for trucks, primarilly 20" calibrations. depending on the truck 275/55/R20 calibrations are avail, but for gassers only. GM HAS NOT CHANGED their position on the Duramax, say you have 265/75/R16 tires, they will only let you change to a 265/70/R16 calibration. It is a liability factor to prevent roll overs. You can't blame them.... when WE THE PEOPLE sitting on the jury's giving judgements for spilling coffee in your own lap. WE THE PEOPLE are the ones to blame for the tight restrictions, and untill WE THE PEOPLE start taking responicbility for our own actions.....no matter how stupid they might be, it will never change........


I know exactly where you're coming from.


We have so many wonderful things to thank our lawyers forhttp://www.dieselplace.com/forum/smileys/Ermm.gif


GarEdited by: biggar

GM needs better lawyers, buying into paranoia fuels the fire my peeps.

Truck is going back into the dealer next Tuesday, they still don't have access to the Bulletin posted above and want me to bring in all the information that I have.


Thanks a ton to this site! Hopefully I can get some resolution to this soon and if I do I will be sure to post back with my findings.

I don't think i read that this voids the warranty though, just gotta put on the 245s to get service for the listed concerns.

Where did everybody go?? Yesterday I bought a brand new LLY, (see sig), and part of the deal was to put 265's on., now after reading this, I guess I'll have him do nerf bars instead until I find out about the tires! http://www.dieselplace.com/forum/smileys/Cry.gif


My 1st post, by the way, glad to be here! I've been here 10 min. and I've already learned a few things !!

Well , the dealer said that they had some new Tech II programming to redo my speedo/dic for 265s and they did it. Now i have since picked up a GPS and check the speed with it and it IS off ! At 77mph the GPS says im doing 80mph ! It is about 2mph off at 60 and gets worse the faster you go. I beleive the GPS is supposed to be pretty accurate . Im sure the DIC and odometer are also so off but havent had time to figure yet. Just my .02 cents ....

Fastoys, sounds exactly like what I have. The difference in tire height is 3.9%, so that adds up perfectly with what you are seeing, as 3mph is 3.9% of 77mph, which adds up to your 80!


I'm heading into the dealer in the morning to see what they can do now, I have little hope they will be able to do anything at all, especially see as they have not seen this service bulletin and can't seem to get their hands on it yet!


But maybe, third times a charm right?

Yeah , no doubt ! So how do i figure my mileage correctly by hand then? Do i use some kind of calculation? 3.9 x pie x hair x earths gravitaional pull >? LOL http://www.dieselplace.com/forum/smileys/Big Smile.gif Does anyone know? Thanks

Not to throw gas on a fire, but I'm kinda glad I've got a gasser with the L480. 285's with no problem. Dealer thinks they're cool and has no problem working on the truck.


OK..."flame suit on"...as they say....

OK, truck is back from the dealer. As expected they talked with GM engineers this AM and confirmed what I have been telling them all along and that is that it CAN NOT be reprogrammed. By this I mean GM is not allowing it to happen, and the only way to do it is with an aftermarket programmer. The do allow the update for the ABS related to the tire size, but not the speedo. We also tried to program my truck with 3500 single axle (because this truck comes with 265's) software and the ECM does not accept it because the VINs don't match.


With that being said, does any one know if any LLY programmers are out yet? Is there any way I can get my truck reprogrammed without spending mucho bucks on a programmer? I can live with the speedo/odometer being off, but what is annoy is the one side effect of the speedo being off is the cruise is all over the place. If you give it 1 mph more then it accels 1.039 mph and then tries to slow down and goes past it and the slowly comes into where you asked it too. Kind of gets annoying! This is the only reason why I want my speedo updated.





In order to calculate your mileage with 265 tires (if you have 245s before) here is the calculation:


(mileage x .039) + mileage / gallons at last fill up provided you fill up each time.


ie, 300 miles driven, 16 gallons


300 x .039 = 11.7


11.7 + 300 = 311.7


311.7/16 = 19.48 MPG





With this being said, does any one know how the DIC measures gallons of fuel used? I am curious how this is done and how accurate this can really be?





In regards to the 6.0 Gasser....I drove one for a day while my Duramax was being looked at for speedo concerns. That truck is a dog compared to the diesel! I got waxed off the stop light by a V6 Explorer! That Duramax would have smoked him but I was left wondering why any one would buy such a truck! Plus the mileage sucks, I only had 12 mpg on a normal drive where I would have gotten closer to 17mpg with the diesel.Edited by: Grabs

Ouch.....Ok Ok I deserved it....Especially on a site like this...