I also posted about this on TYF, but there always seems to be someone on here that has the answer.

I recently took delivery of a brand new 2018 Chevy Tahoe PPV ("police package"). I had a set of takeoff 20" wheels and LX20 tires installed by a wheel shop. I took the Tahoe to my dealer to have the computer reprogrammed for the new tire size. I did the same thing on my 2015 PPV and the dealer was able to do it without issue. After 90 minutes of waiting, the service advisor came back and said it was impossible, that GM could not/would not provide them the "codes" to do it and that was it. I didn't stay around and argue because I went straight from work when they opened and needed to get home and sleep. At least they didn't charge me.

So my question to the SF brain trust is whether or not this makes any sense, and if it does, what are my options? I've started looking at aftermarket programmers and have considered, but my preference would be just to get it done by the dealer. I am waiting for emails from a couple programmer companies. Leaving it wrong is just not an option. The speedometer and odometer are about 10% off and that just isn't going to work. Does anybody have any thoughts?

If there is a genuine reason for this, the dealer can (or should) put you in contact with the zone rep for your area. If they balk at that, find another dealer.

quote:

Originally posted by Oldrider:
If there is a genuine reason for this, the dealer can (or should) put you in contact with the zone rep for your area. If they balk at that, find another dealer.

Over the summer, paint starting peeling off my truck. I took it to the dealer and they said it was out of warranty. I asked for the Regional Zone Rep and the service tech told me they had no way to contact them. No phone number or email. I went on the internet, found the site, emailed the Regional Rep and was called back within 24 hours. It's hard to get some people to do their jobs.

Being it's a 2018 they may not have the ability to reprogram yet.

Not a tech but I follow such things as I once was. GM put the kibosh on dealer reprogramming so you might be out of luck. As I understand it to make a change like this the tech calls a hotline and gets some sort of code from the mothership to allow the reflash to happen.

Programmers will work but you run the risk of having warranty issues. Even though you're just changing the tire size if you ever have a major failure GM will require a screenshot of the diagnostic tool showing the calibrations loaded into the PCM (basically a bunch of alphanumeric codes that stipulate various parameters). Even if you flash back to stock, the PCM keeps track of flashes and if the number is unusually high and there is no record of official reflashes than GM will deny the claim and you'll need to take them to court potentially. The law is on your side here but you still have to spend time and money to prove the case.


All that said, where are you arriving at this 10% figure from? If you are just doing the math to get a difference in diameter of the old and new tires, check your speedo against GPS or a phone app. Usually the overall diameter of the tires does not change much on factory option tires going from 17s to the 20s.


If the difference is already proven and living with the difference is a no go, then the aftermarket is the only option.

The 10% figure is based on GPS and radar comparison. The radar part fortunately being an employment perk and not from getting pulled over. It's also the same variation my 2015 had. There is actually a pretty big difference in overall tire size between the police 17" wheel and tire combo and the 20" combo on the LT and premier. It reads 65 at 72 or so and 30 at 33 or so.

What you're saying about GM releasing codes is basically what the dealer said. On my 2015 they claimed they did it once and they did not. The second time they had it for four hours and got it done. They made it sound like it took some doing.

I'll look at contacting the regional guy. Otherwise I've seen options for an inline speedometer calibrator from Hypertech that doesn't involve a reflash and can be unplugged for service.

I know one of the companies that makes gauges for performance applications made one that was GPS driven so you wouldn’t need to rely on a vehicle speed sensor signal. Might be with consideration.

Look at the bright side. You'll accumulate mileage at a lower rate than normal.

What kind of "first responder" are you? I don't have an answer for you, but the suspension on the PPV's is a pretty specific set up.

You could try Chevy customer service, if some info will shake loose for you that is the way.

Since I retired from GM dealerships last year the ability to get to the bottom of things has left.
Only theory I have is that it is related to your vehicle being a PPV.

I'm ASSUMING and only an assumption is by entering the VIN in the terminal there are a list of "acceptable" changes that can be made to the physical vehicle. I'm going to go out on a limb here and say that it is probably related to tire issues, in other words the replacement 20" tires may not have the same speed and weight rating that the original equipment tires have.

We used to do a lot of wheel and tire upgrades as dealer accessories were a popular item. I can't see GM not allowing tire and wheel changes across the board, too much of a cash cow for them and their dealers.

Again, only a guess but you might call the shop and ask them if it was because the tire and wheel size were not certified due to the VIN. If so, you will probably have to put a "cheater" on your Chevy because there will be no way around the VIN issue. Well there may be but with the integration of components in new vehicles that require reprogramming, even to the point that some power window switches require that today, I do not recommend it. The grief that it could cause........

The issue may be the year, I can plug in with an aftermarket scanner and change tire size on most vehicles, it usually does not require anything from GM or other manufacturers. Most newer vehicles require you to be hooked up to a factory server to change tire sizes and add options, then a reflash to let all the modules on the vehicle know those changes were made.

The tire speed and weight rating could give us fits when we had a used car come in that was "personalized". Last one that comes to mind was an Escalade with 22" wheels on it. Tech wanted price on two tires as two were almost new. So we look at the VIN first and see it was produced with 20" wheels. Look up the tire and wheel combination via VIN.

Tires on the vehicle were of less weight capacity and speed rating than what was originally on it. A big no-no for liability reasons. Used car was not too elated when they found out that they now needed four tires.

Same issue came up with tire dealers that would sell tires based on price, not what was correct for the car. Saw a lot of that too.

As much as I appreciate the sentiment that I would be accumulating mileage slower, being off by 5000 miles or more by the time I would consider selling seems dishonest and the juice certainly isn't worth the squeeze as it relates to having to forever compensate for the variance.

quote:

Originally posted by BigSwede:
What kind of "first responder" are you? I don't have an answer for you, but the suspension on the PPV's is a pretty specific set up.

You could try Chevy customer service, if some info will shake loose for you that is the way.

I'm a police officer. This 2018 PPV and the 2015 PPV that preceded it were bought new via a law enforcement pricing program that required proof of employment, etc.

quote:

Originally posted by Jaywendland1981:
The issue may be the year, I can plug in with an aftermarket scanner and change tire size on most vehicles, it usually does not require anything from GM or other manufacturers. Most newer vehicles require you to be hooked up to a factory server to change tire sizes and add options, then a reflash to let all the modules on the vehicle know those changes were made.

Any suggestions on the aftermarket scanner to use? I have seen a variety of tuners and speedometer calibrators online. I have no interest in a full "tune", but I've noticed most of the speedometer tools are VIN locked to the vehicle they last programmed, so if there is something where that isn't the case it might be worth a premium to me.

quote:

Originally posted by shovelhead:
The tire speed and weight rating could give us fits when we had a used car come in that was "personalized". Last one that comes to mind was an Escalade with 22" wheels on it. Tech wanted price on two tires as two were almost new. So we look at the VIN first and see it was produced with 20" wheels. Look up the tire and wheel combination via VIN.

Tires on the vehicle were of less weight capacity and speed rating than what was originally on it. A big no-no for liability reasons. Used car was not too elated when they found out that they now needed four tires.

Same issue came up with tire dealers that would sell tires based on price, not what was correct for the car. Saw a lot of that too.

Tire size and weight capacity are fine. These are OEM specified takeoff wheels and tires for the non police Tahoe. The speed rating is not as high as the police package tires. Not a concern to me since I think I've had the 2015 over 80 MPH twice.

I come back to being frustrated that it "could be done" on the 2015 but apparently cannot on the 2018. I will reach out to GM customer service as several have suggested.

Not that this is helpful, but I could completely understand GM and the dealer not supporting a tire change in a PPV sold under a PPV program that have a reduced speed rating.
I wouldn't do it either. But in any case the zone rep is your source of the official word on the issue.

quote:

Tire size and weight capacity are fine. These are OEM specified takeoff wheels and tires for the non police Tahoe. The speed rating is not as high as the police package tires. Not a concern to me since I think I've had the 2015 over 80 MPH twice.

Right there is the answer, speed ratings.

While I understand your point but please understand this from a product liability standpoint. And I'm just throwing numbers out here as I do not know the speed ratings of either of the tires or the speed limiter or lack of speed limiter in the PPV or the non PPV.

General Motors a number of years ago sent dealers a TSB stating that Partech (GM's tech assistance for dealership use only) will not assist a dealership in any modification of a vehicle with a part or accessory that was not originally intended for that vehicle. Modifying a vehicle whether using a part not intended or an accessory not intended for that vehicle could affect EPA certifications, FMVSS Compliance, serviceability, warranty and product liability issues at a later time. Any and all modifications to a GM vehicle not approved by the manufacturer is at the dealership and personnel involved risk and liability. Not the exact wording but close enough to get the point across.

When dealership personnel call in with a technical question the first thing asked is for the VIN number, setting the electronic parts catalog and to verify which RPO's (build options) on the vehicle. For example, your PPV is equipped with rubber floor covering instead of carpet and you want carpet instead. (Your PPV might have carpets, just guessing as I have not worked with the PPV's only 9C1's from days long past, just as a example)

So I go to the catalog and look up carpet and for some reason, maybe the floor console is different, nothing seems to look right. Maybe the carpet listing shows as "P/N 99999999, Carpet, front floor, CK106, Black, AM6, D55 (exc PPV).
Roughly translated: Front floor carpet, two wheel and four wheel drive Tahoe/Yukon, black color, front bucket seats, with floor console, EXCEPT Police Pursuit Vehicle. So? Difference? Scratch head, call into Partech, first thing they will ask you for is the VIN, to set their catalogs and have the vehicle build in front of them. So you request help in finding a floor carpet as the customer wants to replace the full floor mat. And you know what you will hear?

Partech will tell us that you are attempting to modify a vehicle contrary to how it was designed and certified and they cannot assist you and immediately terminate the call after giving you a reference number for the call in. No pleading, going to higher level, you are done and off the line. Even with something as innocuous as a carpet swap, nope, liability, even though the floor pans and carpet retainers are the same part number, you are modifying a vehicle. If a lawsuit comes up involving anything remotely related to that carpet being changed from original you can bet that some attorney somewhere will jump on that looking for the most and deepest pockets to dig into.

Another example, new body Camaro. One of our counter persons sold a set of 3.73 gears. GM made a package in the Performance Parts line with a number to call in for calibrations, installing dealer had a special code in the kit to use. The gear kit was on backorder so he got the idea to sell them by looking up the parts for the current model car with 3.73's. The car can be ordered that way, the aforementioned car had 3.23's. So he sells the individual parts, ring and pinion and hardware, all parts of the kit. Except for the code. So he calls in and is told that the code is only included in the retrofit kit, without the number he will not get the download. Tried everything he could do. I tried a couple long time contacts that I knew to get his azz out of the fire. No luck, my contacts said that their hands were tied and he was out of luck. That whole thing got ugly, it had to have a custom dyno tune done to it, aka big bucks........

Sorry to be long winded, but good luck.

All logical to me. The only thing through all of this that I can't figure out is how they were able to do it three years ago and not now, particularly given that this is the same generation vehicle.

It sounds like an aftermarket solution is the ticket.

quote:

Originally posted by DaBigBR:
All logical to me. The only thing through all of this that I can't figure out is how they were able to do it three years ago and not now, particularly given that this is the same generation vehicle.

It sounds like an aftermarket solution is the ticket.

I’ll try to find it tonight but it was literally a change in policy in the past couple years. I think there was a TSB announcing it but I may be off.

Snap On scanners have been really good at having the tire size change option, heck just find an independent shop and ask them to plug in and see if they can change the size. Most shops would at least do that free of charge. Autel scanners have quite a bit of factory functions as well.