Offroad Trailblazers and Envoys

Possible Speedometer and Abs fix for gear change

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by Jrgunn5150 » Tue Jun 14, 2016 7:15 pm

My ABS/Stabilitrack never worked, and I never got the chime. Maybe try unplugging the module under the driver's floorboard?
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by Shdwdrgn » Tue Jun 14, 2016 7:51 pm

No, like I said above it's possible to reprogram the P10 PCM, you just need a VIN that had the 4.10 gears stock, like this one: 1GNDT13S242164315 (2004 trailblazer)
I had the dealership program that VIN into my PCM, then I used HPtuners to change the VIN back to my original. From there you can copy over any tables for tuning. The funny thing is, the data that HPT copies in their tune files contains the gear info, but nobody can figure out the actual bits that need twiddled to make it happen. So just by using HPT tune files, I can make mine go between 3.42 and 4.10 gears. I have a tune file saved that has all the factory settings for 4.10 gears, but also is set for larger tires so the speedo almost perfectly matches my 30.6" tires. I've been running this for over 2 years now, never had a single ABS issue, and everything is working as expected.
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by v7guy » Tue Jun 14, 2016 9:52 pm

I realize that, and that's great, but it doesn't help the guys with 4.56s or in my case 5.13s and with tires much larger.

Since the twidly bits haven't been figured out were essentially stuck outta luck.
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by Shdwdrgn » Tue Jun 14, 2016 10:25 pm

Certainly we can't set the gears to non-stock ranges, but on the other hand changing to 4.10s in the PCM might be enough to keep the ABS from going nuts?
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by Jrgunn5150 » Tue Jun 14, 2016 10:36 pm

I think unplugging the box would do it, unless the goal is to keep it functioning.
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by v7guy » Wed Jun 15, 2016 12:50 am

Jeff- It really is a good work around for the stock gears, it's very encouraging. It's a shame it hasn't expanded to finding out exactly what GM did in the early pcm. For the vast majority of people I'm sure this will be a good solution. Is there a place you can host the files so other guys can copy your procedure?

The only other guy gearing higher than 4.10s that I can think of is Moots and he has an 06 and apparently no issues. So I'm largely alone in this pursuit at this point

They did a lot of strange things with the early pcm that guys haven't been able to figure out, so I'm not sure this should be much of a surprise.

Personally, I made an effort to retain ABS, and until I got over 40mph it seemed to have worked LOL

I found a cheap 06 wiring harness on eBay and I've got an 06 pcm from an I6 trailblazer on the way. It's headed out to Jeremy at limeswap to get an 04 tune as soon as I get it. Other than adding an 06 gauge cluster and moving 6 wires on the 06 engine harness and the ECT plug it should be plug and play and allow all the benefits the 06 has.
Neither Jeremy or I have any idea if it'll keep the abs happy, I suspect not, but I'm gonna give it a go and see what happens... may have to swap out to a 4 channel setup if I want ABS to function and if it gets to that point I may give up.

At the minimum I should be able to have the speedo read correctly and control electric fans. If it turns out none of it works I'm out a lil money and time, I'll just put the 04 stuff back in.
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by Shdwdrgn » Wed Jun 15, 2016 10:25 am

You can find my HPT files here: http://sourpuss.net/projects/vehicles/trailblazer/hpt/
Note that the one marked 'shdwdrgn' has a lot of adjustments for my engine, so I would NOT recommend just applying it straight to another vehicle, however you'll want to look at how I changed shift timings and pressure. Those tables give a firmer shift but also adjust the timing quite a bit into a range that I found more similar to my own driving style.

After all the work to convert to a P12, I wouldn't even consider going back. As noted, the P12 has quite a few more features that you can modify. I'd love to do that to mine, but I just don't have the time or energy these days.
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by v7guy » Thu Jun 16, 2016 4:35 am

I don't anticipate there being any major issues with the P12 swap. I've chatted with another fella that had it successfully running and he confirmed what I'd figured out staring at wiring diagrams for the 04 and 06. The gauge cluster he never resolved... He moved on to another vehicle before he figured it out. But apparently the 04 cluster shows fuel empty when full and full when empty, the the voltage read backwards the abs light staid activated etc. It appears the cluster swap should fix it assuming the plug is the same... and I'm reasonably sure it is. But I don't think I'd be content with it if I had to live with that permanently. It's likely something that would make me swap back.

I've started pictures and a write up for the P12 swap, it seems like it would be helpful to a lot of people, so if I can figure it out it'll be well documented.


Was there anything else you had to do to get the gear program working? You literally just load up the VIN, copy in the file, then switch the VIN back to the one for your vehicle? It seems almost too easy LOL
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by Shdwdrgn » Thu Jun 16, 2016 9:06 am

If you have HPtuners, you should be able to skip the dealership and just write my 4.10 stock file to your PCM, and it should just work. Problem is, nobody has actually followed through on trying it out, so I don't know if there are any caveats to the process, but I did flash the file to my own second PCM and the gear change followed. So all you really should need to do is load up the 4.10 file, change the VIN to match your vehicle, then flash it to the PCM, and that should be it.
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by larryk » Fri Jun 17, 2016 9:58 am

If my latest tune from PCMforless doesnt fix the gearchange issue, I am going to be trying the Jeff method to update my spare PCM with HPTuners to the stock GM 4.10 calibration file. Im pretty sure his method is 100% legit and will fix the issue.

FWIW, I had swapped my 2004 cluster a long time ago for a cluster form an 06 SS. It dropped in perfectly....no issues with any guage, and even the speedo read perfectly (strange, as the SS was a 4.10, and mine was a 3.42....so I guess the speedo gets its reading after the PCM converts it in both cases).

The only thing I would wonder about swapping over a 2006 PCM from the 2004.....is the change from the Class2 bus in the 2004, to the CANbus in the 2006. There are so many damn modules in these trucks that talk over the bus to each other, that I dont know if swapping over the PCM would impact the functioning of the other modules. Has anyone ever confirmed that the communication bus of the two PCM's is compatible? I know in my new Camaro there are three (!) different busses which differnt components hang on....high speed, low speed, CAN, etc.
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by TBYODA » Fri Jun 17, 2016 8:12 pm

GM didn't change to the CAN bus in the I6 until 07.
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by v7guy » Mon Jun 20, 2016 1:28 am

Yup, Robert is correct, the 06 still communicates over serial data, and I know of at least one fella that's confirmed it in actual application.

It was his comments about the cluster that made me believe it was an issue, as well as Jeremy at limeswap saying it doesn't look like the 06 cluster and 04 cluster are compatible. I haven't checked myself.

I did find many instances where guys said there was no issues during a direct swap between the newer and older clusters though, so I'm not sure what the actual problem is. Maybe an issue with the pcm swap itself? Maybe the guy that did the pcm swap had a bum cluster? It's something I don't look forward to tackling.
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by rScherzer » Tue Dec 13, 2016 11:14 am

Shdwdrgn wrote:If you have HPtuners, you should be able to skip the dealership and just write my 4.10 stock file to your PCM, and it should just work. Problem is, nobody has actually followed through on trying it out, so I don't know if there are any caveats to the process, but I did flash the file to my own second PCM and the gear change followed. So all you really should need to do is load up the 4.10 file, change the VIN to match your vehicle, then flash it to the PCM, and that should be it.


I may try this option.
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by rScherzer » Wed Dec 14, 2016 1:26 pm

I ended up flashing the VIN 1GNDT13S242164315 last night that Shdwdrgn had posted earlier. Today I shipped out the ECM to be programmed with a aftermarket tune. I'm thinking the ABS is going to have a hay day with the stock 3.73 gears. I'll just pull the fuse until I get the gears swapped out.
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by rScherzer » Sun Dec 18, 2016 11:26 am

So I got my PCM back and installed it. Went to drive it home and the Service engine soon light had come on. I had two codes set, First one was bank one O2 heater and the second one was for the catalytic converter P0420. The cat code was suppose to be programmed out of the PCM. Looking at the PCM from my scan tool I also noticed when I used the 04 vin 1GNDT13S242164315 it had added Secondary air injection and a few other smog related checks. I need this to pass a emissions test and my 02 didn't come with secondary air or a EGR valve. I looked in to the old PCM I had and the only monitors (I/M flags) it had were Cat O2 and one other that I cant remember. I spent a few hours looking for a VIN that had the same emissions calibrations as I did and the 4.10 calibration. Now all I have left is to call the tuner tomorrow and hope they will help me straiten this out with out paying full price again. On a much more positive note the aftermarket tune made the transmission shift a lot nicer! As for power we have I and stuff on the road so I am unable to tell a difference there.
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by Trail X » Mon Dec 19, 2016 10:18 am

v7guy wrote:The only other guy gearing higher than 4.10s that I can think of is Moots and he has an 06 and apparently no issues. So I'm largely alone in this pursuit at this point


Hey now, don't forget me!

I pulled the fuse on the ABS and haven't looked back. When I go in for inspection, I plug the fuse in, which makes the ABS light happy as long as I turn off the ignition before the inspection.
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by rScherzer » Mon Dec 19, 2016 3:23 pm

Trail X wrote:
v7guy wrote:The only other guy gearing higher than 4.10s that I can think of is Moots and he has an 06 and apparently no issues. So I'm largely alone in this pursuit at this point


Hey now, don't forget me!

I pulled the fuse on the ABS and haven't looked back. When I go in for inspection, I plug the fuse in, which makes the ABS light happy as long as I turn off the ignition before the inspection.



Strange when I had the PCM with the 4.10s in The ABS light never came on. I even went and slide it around on some ice to activate the ABS pump. all seems good. Same when I had the 3.73 programming. Beside all that I just got off the phone with the tuner guy and apparently there was a mix up on my ECM so now its headed back to North Carolina to get sorted out. As for emissions, i had found a vin that only has Cats, EVAP O2 sensor and O2 sensor heater flags. Heres RPOs are EVA FE9 and NF7. Also had GT5 (4.10 calibration) 1GNDT13SX22176855
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by Shdwdrgn » Wed Dec 28, 2016 11:30 am

@rScherzer - so what happened when you flashed my PCM file? And I'm confused between your posts -- are you running 3.73 or 4.10 gears? As for the various sensors that your truck doesn't have, there is a table of all those tests, you can turn them on and off individually to suit your equipment.
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by Anthony Hernandez » Wed Dec 28, 2016 12:52 pm

My '07 hasn't gotten pist off yet with the 4.56 swap, lucky I guess.
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by rScherzer » Wed Dec 28, 2016 5:23 pm

Shdwdrgn wrote:@rScherzer - so what happened when you flashed my PCM file? And I'm confused between your posts -- are you running 3.73 or 4.10 gears? As for the various sensors that your truck doesn't have, there is a table of all those tests, you can turn them on and off individually to suit your equipment.


I ended up using VIN from a 02 Trailblazer that came factory equipped with 4.10 gears and the same emissions equipment. My Trailblazer has 3.73 gears. (I plan on putting 4.10 in it) I wish I had the HP tuners setup, I would have flashed it myself.
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