How to update computer to match gear change?

[HARDTRAILZ]

I did notice he had an 04 pcm...I actually acknowledged that in an earlier post of mine in this read. I am fully aware of the issues with reprogramming aftermarket tire sizes in the earlier pcms but I have never heard of issues with programming for gear ratios. Since 02-05 GMT360's came factory with 4.10 gear ratios, it "simply" does not make sense that it's not a programming option.

You can unruffle your panties now sir

If there was a simple gearing ratio change it could be used for tire size changes as they basically do the same thing and either parameter could help get speedo and shift points in line. Simply...neither has been found over the years either by PCMforless or a member. I am quite certain PCMforless has taken a good look since it seems to be an extremely common question to them with the hundreds of pre-06 lifted ones out there.

 

[Shdwdrgn]

Actually it has been asked several times on the HPTuners forums. The last reply from HPT was about 2 years ago, saying they were looking into it. I haven't seen a response to any of the queries since then.

 

[Shdwdrgn]

Finally got the front diff swapped out this weekend... OMG what a PIA to do by yourself! Anyway, mechanically I am completely converted to the 4.10 gears now. Still threw an ABS error on the way in to work yesterday, and I still haven't found any solution to reprogramming for the new gears. Anyone else care to chime in?

 

[Shdwdrgn]

*bump* Still looking for anyone else with HPTuners. If you have 4.10 gears, or even 3.73 gears, and would be so kind as to send me a file of your full PCM read (not just the calibration file), I would appreciate it. I am curious to see if either one makes a difference in my issues, because that would tell us if the code is even located in the PCM.

 

[jimmyjam]

Just FYI: if someone sends you their hpt file, you won't be able to flash it without buying two more credits. download a tune file from the hpt repository and try loading it/writing it and see

 

[jrSS]

Those credits are fucking expensive.

 

[Shdwdrgn]

Just FYI: if someone sends you their hpt file, you won't be able to flash it without buying two more credits. download a tune file from the hpt repository and try loading it/writing it and see

Erg, really? I assumed it would be similar to flashing a tune file -- that it only mattered what PCM I was writing the code TO. Seems like if the tune file was going to change the gear ratios, somebody would have noticed that by now and commented on it when trying other people's tunes.

 

[jimmyjam]

you probably haven't seen anyone do it because it would cost $100 just to try. unless you had a year/model license

in reality hpt gets licensed to the VCMID, not the VIN...

i think efilive can do what you want, not sure

 

[Bz07]

I'm making the rounds on various sites to see what answers I get on this, because oddly enough, it doesn't seem like this is something many people have actually done?

I am changing my gears from 3.42 to 4.10, and if I don't tell the computer (not sure if its the PCM or TCCM that handles this) about the change, everything from my speedometer to the transmission is going to be off by nearly 20%. Now obviously GM has some way of programming in which gear ratio is installed in each vehicle -- the problem is that I called my dealership and nobody there had ever done such a change before, and they had no idea how to reprogram my system without calling a GM tech line (for which they would pass on the charges to me for using this service).

I also have HPTuners available, and I was given a suggestion on changes to test after I swap the axles. This seems more like a hack than an actual correction, but I'm willing to give it a try and see what happens.

The rear axle is going in on Saturday. The front axle will follow in a week or two, depending on how ambitious I'm feeling. Any info that can be provided in the meantime for a *proper* correction would be appreciated.

I'm guessing you got it figured out. I probly fixed itself when you Change the front Front gears. If Speed sensors were on each wheel it would have been fine, Your problem was you rear Drive shaft was spinning much faster because of the Lower gears, And the front was reading the actual wheel Speed. I'm assuming that's what happened

 

[djthumper]

You do realize this thread has not been posted in over 4 years. Your answer is the obvious one and it does nothing to resolve this. The PCM is not programmable on the older TBs to adjust the gearing. He had upgraded both sets of gears to match.

 

[Bz07]

Yeah I didn't see that date, I thought you could use an aftermarket programmer to Change your tire size and the gear ratio, unless it's old enough that it has an actual gear in the transmission for the speed sensor. , If he has the same tire size And gear ratios front and back then I probly has a bed sensor triggering ABS. I was just looking around. I changed gear ratio On 07 Silverado classic half ton 4x4, I went from 342 to 373 with stock tire size, I don't think my shift points are off too far but my speedometer is off by about 8 at 60. Just trying to find out what the best tuner to buy for that would be. Right before I did this I called the dealership and they told me they could do it for $150, And I also looked into a hypertech programmer for about $330 that could also do it. I called the dealer to get it done and the mechanic this time told me that they can't do it and they didn't know of any aftermarket Programmers they could

 

[djthumper]

This is in the GMT 360/370 forum. They are different then the Silverados. You need to go to the Full sized forum for information on the Silverado.

 

[Dirtyhart89]

I am having the same issue as I just replaced the rear end with a 3.42 posi from the oem gt4 now my colorodo is throwing p0894 code trans comp slipping, what exactly did you do to fix this issue shdwdrgn bc it is a real pain in my rear end ...get it ? Haha stupid pun 🤣

I'm making the rounds on various sites to see what answers I get on this, because oddly enough, it doesn't seem like this is something many people have actually done?

I am changing my gears from 3.42 to 4.10, and if I don't tell the computer (not sure if its the PCM or TCCM that handles this) about the change, everything from my speedometer to the transmission is going to be off by nearly 20%. Now obviously GM has some way of programming in which gear ratio is installed in each vehicle -- the problem is that I called my dealership and nobody there had ever done such a change before, and they had no idea how to reprogram my system without calling a GM tech line (for which they would pass on the charges to me for using this service).

I also have HPTuners available, and I was given a suggestion on changes to test after I swap the axles. This seems more like a hack than an actual correction, but I'm willing to give it a try and see what happens.

The rear axle is going in on Saturday. The front axle will follow in a week or two, depending on how ambitious I'm feeling. Any info that can be provided in the meantime for a *proper* correction would be appreciated.

I am having the same issue as I just replaced the rear end with a 3.42 posi from the oem gt4 now my colorodo is throwing p0894 code trans comp slipping, what exactly did you do to fix this issue shdwdrgn bc it is a real pain in my rear end ...get it ? Haha stupid pun 🤣

 

[Mooseman]

This is a long dead thread. Most of the people in it haven't been active for a long while.

This thread/section is regarding the GMT360 platform (TrailBlazers, Envoys, etc). We do have a section for your platform however info in it is scant.

P0894 is a transmission issue, likely the Torque Converter Clutch slipping. Since you went with a taller, numerically lower, gear, maybe the TCC is having a harder time holding and is coincidental to your gear change. Or because of the changed gearing, the computer is expecting a certain RPM vs speed and thinks it is slipping. I have no idea what PCM you have or even the year of your Colorado. If it's the same P10 PCM as the 02-05 TB, the gearing is not modifiable directly, even with HPTuners. It might be modifiable updating the PCM via Tis2000 and a Tech 2 using the VIN of a same year Colorado with the same gearing, which should also correct your speedo.