Any GM Techs out there?

ncjeepers

Well-Known Member
Joined
Apr 13, 2005
Location
Locust, NC
I just changed the gears in my '06 Chevy Express 3500 van from 3.73 to 4.10 for towing. I'm assuming the PCM needs to be updated. Problem is, posing that question to most any dealer service department just gets a blank stare.
Are there any GM Techs out there that can help me?
 
I'd like to think the dealer could reprogram the pcm for the different gears as long as they were a factory option but not sure.
 
Yeah, you'd think so. I've talked to a couple different service writers and they are clueless. I might just have to take a ride out there and sneak into their shop.
 
When I was a dealer tech, $20 and a six pack was my under the table fee. May wanna troll around the shop around 11 or so. Techs need lunch money...
 
If you cant get anywhere with a dealer you could look into a programmer and have the advantage of of a little more power and be able to change your speedo for gear ratio or tire size. A quick search does show that a few different ones are available.

Buckeye Performance Inc.
828-779-2242
 
There should be plenty of guys that tune out your way. It'll probably be 100 to 150 or so, but they can do it. If you go that route, get them to tune it for you while they're at it. More power it always better.
 
Not sure about a 2006. On the 2002 0411 the tech 2 can change tire diameter not gear ratio, at least from the main menu. However, what you need would be well within the realm of tire diameter size.

Whoever did the HPT or EFI live change would have to make sure they got it right or they would have to tweak it until it worked. If you change gear ratio in the ECM and have a different size tire programmed in the BCM, you could get an ABS light for an axle ratio mismatch. Been there. Done that. I tried to fine tune a "tune" for a change in tire size and couldn't do it.

You can only do the change in one spot. I prefer the tech 2 if you can get a tire size that works out. Easier to test and tune unless you have the timing software.

Another option is one of the inline electronic units for speedo calibration.

The front door of the dealer Svc dept usually won't have a clue.

Where are you located. I don't own the tool myself but have a dealer tech friend who let's me borrow the tech 2 from time to time.
 
To the best of my knowledge (at least in the PCM that the trucks use and I assume the vans use the same ones) there is an acceptable range on the tire size, up to a 285/75-16 or around 33" . When I went to 37s on my Silverado, I used my HP Tuners to get the speedo corrected and compared it to a GPS speedometer app on my phone which is very accurate. HPT is very picky on the tire size, you basically have to measure the tire height as closely as possible and can't assume a 37 is a 37. Mine are 36.22" tall. However, I learned that you only correct the VSS which is the speedometer pickup as well as the rear ABS sensor. What it doesn't do is correct the front ABS sensor readings and that's why my ABS and Parking Brake light will pop on from time to time while I'm driving down the road. I assume that it thinks the rear is turning way fast than the front and after a certain amount of time or distance, it throws a mismatch code and pops the light. I would need to get my hands on a Tech II to properly fix it.

In your case, you would probably be fine with either method of correction.
 
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