PCM SUCCESS!!!

[Shdwdrgn]

Took my truck in to try programming from a different VIN today, and it appears we were successful in finally getting the gear changes made. The tech informed me that he was not able to pull a VCI from GM, but when he put this VIN into his programmer, it was able to pull up the code and make changes to my PCM that included the correct gear info.

For future records, I used this VIN: 1GNDT13S242164315
(It might be nice to start a collection of VIN numbers including what gears and features they had?)

This is from a 2004 LS TB 4x4, SWB with GT5 (I have the full RPO list printed out here). The vehicle was salvaged and crushed last Fall. Unfortunately that's about all the info I have. The page that the tech printed out for me does not contain any real data on what changes there were between the programming. Basically what he told me was that he pulled the build for this VIN with a tool he has on his desktop computer, and used that to rewrite the PCM.

Quite frankly, the tech was surprised it worked at all. The PCM currently still has this other VIN number in it, which of course does not match the proper VIN of the vehicle, yet he said it didn't give him any error codes or even require a security re-learn. The VIN above was also built for a vehicle with 17" wheels, and mine has 16", but he found a tire size that was very close, and my speedometer is within 1mph at 55... I can live with this!!!

By the time I got home, the system had (of course) set a P0410 code, so I used this as my first test for reprogramming with HPTuners... I disabled the code again, took it around the block, and confirmed that the speedometer was still correct. I won't have time to work on it tomorrow, but this weekend I will be. The first thing I want to do is use HPT to reset the VIN in the PCM back to the *actual* VIN of my vehicle. Even though it hasn't caused problems yet, why take chances? The next thing I will be doing is going through all of the programming again from scratch and re-applying all of the adjustments I had previously made to the other PCM, with reference to any changes I happen to see between the old and new settings. It will be interesting just comparing what tables have actually changed between stock versions with the 3.42 and 4.10 gears.

[v7guy]

This is pretty great news.

I suppose this would also work for guys that change gears and tire sizes that mimics closely a ratio close top a stock option... for instance 33" tires and 4.56 gears mimics a stock truck on 4.10s. Should keep ABS and speedo happy.

Curious if you're going to be able to pull the pertinent info from the pcm so that we can just change the tables.

Thanks for being stubborn enough to find a solution!

[Trail X]

If you are 2005-, the tire size won't matter for your ABS, only the gear ratio. If you are 2006+ the gear ratio doesn't matter at all to the ABS, so this reprogramming isn't necessary.

But, Jeff, if you can figure out what tables might have changed to allow for the new gear ratio, maybe we can unlock the secrets of changing the ratio to whatever we want.

[Shdwdrgn]

James -

We both have 2004s, so yeah this programming is *very* important for ABS. In fact even though my ABS warning hasn't gone off in a long time, I've been noticing that my ABS braking frequently grinds while backing out of my driveway (very slight downhill slope), and I've heard it grind a few times while pulling in to my drive when I hit the dip at the curb. I would have to say that the ABS system it critically sensitive to change on these older models?

I would love to figure out what tables changed, but I am limited to HPT as my only tool, and I seem to recall that the saves files are encrypted, which would prevent any useful comparison of that data? Since I have two PCMs, I can easily throw the other one with the 3.42 programming back in the vehicle, but I would need access to a tool that could read the raw data from the PCM. I'm more than happy to pull data or try to do comparisons between the PCM data if anyone has suggestions. I can also supply the HPT files from a 'read entire' (I have a copy of the stock 3.42 PCM and now a copy of the stock 4.10 PCM). I also plan on testing the theory of doing a write-entire to the 3.42pcm with the data from the 4.10pcm... just to see if any of that information may actually be captured by HPT.

[Shdwdrgn]

I think I'm going to go insane...

I had a chance to pull out the other PCM today and try doing some programming updates with HPTuners. You guys aren't going to believe this, but I was able to switch my speedometer reading back and forth just by using a calibration write! I even tried loading the 3.42 file and just changing the four parameters on the speedometer page to match what was in the 4.10 file, and that had no effect (speed still read for 3.42 gears). The only thing I haven't checked is the odometer reading -- I have my old PCM in the truck which I wrote the 4.10 calibration file to, and will be checking against mile-markers as I drive in to work tomorrow.

So the good news is that gearing changes CAN be corrected by using a tune file with HPT. And that probably really narrows down where all of these parameters could be hiding. (The bad news is I had to spend a lot of money to figure this out...) I'll be digging into the files when I get a chance, and see if I can figure out anything. I have nearly-stock files from both gears... Besides the gear change, the teach at the dealership also adjusted my tire size, so if I'm able to find any info in the files, I can probably located BOTH settings.

If anybody wants a copy of my tune files (from either the 3.42 or the 4.10 stock files), let me know, I'm more than happy to share. I'll also get these posted on HPT when I get a chance.

[Trail X]

What do the tune files look like? Are they encrypted as you had alluded to before? or is this something different? Is this more or less an editable text file of parameters?

[Shdwdrgn]

OK now you got me curious... I pulled up a hex editor and took a peek. It doesn't appear to be quite that easy... I did a search for partial matches of my VIN, and nothing came up. It will probably take more digging.

[Shdwdrgn]

For anyone who wants to look, here are the (nearly) stock PCM files for 342 and 410 gears. Note that the 410 file was adjusted by the dealer for 31" tires (specifically 255-70-17). I'd love to hear from anyone else to confirm that a simple 'write calibration' from this file works for changing your gears as well. If we could also get a file from a 373 vehicle, at least we could all make gear adjustments without completely screwing our speedometers.

http://sourpuss.net/projects/vehicles/trailblazer/hpt/

[Trail X]

Jeff, have you looked into the .bin format? Apparently that is easier to edit and shows all of the variables that HPT hides. Apparently there are programs from HPtuners that can pull the .bin files pretty easily. I don't have HPTuners, but that's what I got from some quick searching and reading around. Might be worth a shot.

There are also some .bin repositories out on the web, if you're looking for the 3.73 tune.

[Shdwdrgn]

I've dug through the editor, and I see where it will *read* .bin files, but I can't find anything that will *write* a bin file. The only thing I can think of is maybe when I do a read-entire, it might give me the option there, so I'll check that next time I have the computer hooked up.

I did find a reference that the .bin file is a raw format, and that the .ht file is proprietary and compressed. That certainly makes sense with what I've seen, so maybe if I can still get the current version of HPT to save a .bin file, I can make out some of the details.

[Shdwdrgn]

Another update... I sent the information and files to HPTuners with an explanation of what's been going on. Its rather frustrating that I had to explain again that changing the parameters on the speedo page does not have any affect on the dash speedo/odometer (although it does seem to correct the PCM's perception of actual speed). Apparently they have so completely ignored this issue in the past that they didn't even remember that we've been complaining about it.

Anyway, once I explained the situation again, I got an email back saying he was adding this to the engineer's queue. I'm not holding my breath, but hopefully this means someone will at least be looking at the problem again.