How to update computer to match gear change?

[Shdwdrgn]

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.

 

[The_Roadie]

There is indeed an option on the GM Tech II tool to change the ratio. As you found, dealer's don't give it away. Anybody getting larger offroad tires is in the same boat, and EFILive and HPTuners have been attempted with less than total success to tune in the lower number of VSS pulses per mile that larger tires give you. As far as I know, nobody has been totally successful tuning in new tire sizes to adjust the speedometer perfectly.

Eric's the expert - let's see if he sees this thread to post a summary.

 

[Shdwdrgn]

After driving it around today, the abs/brake system warning keeps coming on every few miles. Sometimes I can drive for miles, other times it came on within about 10 seconds of starting to drive. I also have codes now for P0741 (TCC system stuck) and P0894 (Trans component slipping).

The more I drive it, the stiffer the shifting has gotten. In town, its just slamming into gears, even at very light throttle. I reset my shift speeds to about 50% of stock (I was at about 25%). Apparently I need to drive for a bit before I can really tell if the new settings will be right.

 

[The_Roadie]

If you got the rear axle in yesterday with the new ratio, I'm not surprised at the throwing of codes today as the ABS system sees the mismatch. You might be better off pulling the ABS fuse for a week.

 

[Shdwdrgn]

If you got the rear axle in yesterday with the new ratio, I'm not surprised at the throwing of codes today as the ABS system sees the mismatch. You might be better off pulling the ABS fuse for a week.

Can you provide more details about this? Is it an issue caused by the front axle still having a different gear ratio, or because the computer needs to re-learn the changes to the rear axle? Could I get it to learn faster if I pull the power?

 

[Wooluf1952]

It's the different gear ratios. The same would happen if you had big diameter tires on the back and small diameter tires on the front.

I'm surprised the ABS isn't engaging when you brake.

 

[Sparky]

It's the different gear ratios. The same would happen if you had big diameter tires on the back and small diameter tires on the front.

I'm surprised the ABS isn't engaging when you brake.

If he isn't in 4x4 (which with different ratio diffs he should not be!) then the front diff doesn't matter. All the wheels are spinning at the same rate.

The issue is morel likely since everything is off by 20%, everything down to the shift points is all wrong and off far enough for the computer to know something is up. It assumes there has to be some other problem, like the transmission not shifting correctly.

 

[Wooluf1952]

Does the 2004 have 3 or 4 wheel ABS?
IIRC, my 2003 has just one sensor (VSS) for the rear wheels and gets its signal from the drive shaft RPM's. Wouldn't that show up as a conflicting reading if the front and rear diffs had different ratios?

 

[RayVoy]

Does the 2004 have 3 or 4 wheel ABS?

The '04 is a 3 channel, only one channel in the rear. As Wooluf1952 suggests, it should cause an ABS conflict.

 

[DJones]

My 2003 has just one sensor (VSS) for the rear wheels and gets its signal from the drive shaft RPM's.

Mine has two off the rear driveshaft on the transfer case, one on the front driveshaft on the transfer case, and one on each front wheel hub.

 

[Sparky]

Does the 2004 have 3 or 4 wheel ABS?
IIRC, my 2003 has just one sensor (VSS) for the rear wheels and gets its signal from the drive shaft RPM's. Wouldn't that show up as a conflicting reading if the front and rear diffs had different ratios?

Hmmm good point The system is going to be expecting X pulses on that driveshaft sensor for Y pulses from each front wheel.

That would be why bigger tires don't bother the computer much, since that doesn't change the relationship.

I stand corrected.

 

[Shdwdrgn]

All right I've been out experimenting again, trying different things in HPTuners under the speedo tab. I tried changing pulses per; trans revs per; and trans revs/mile, increasing them times 1.199. Then I reset them and increased the final drive ratio times 1.199. Neither had any affect on either the speedometer, odometer, or the abs errors.

I did note that the shifting starts out normal, and it only starts slamming the gears after the ABS light comes on. Once I stop and restart the truck, it shifts normally again until the next error pops up.

Roadie... I don't suppose you happen to know the umber for the ABS fuse, and which box its in? Sounds like this is going to be my best bet, it will be at least 2 more weeks before I have a chance to get to the front diff, and I need to be able to drive to work without destroying my tranny.

 

[Sparky]

J-case fuse #33 under the hood is the ABS fuse (in the front corner near the power studs)

 

[Shdwdrgn]

J-case fuse #33 under the hood is the ABS fuse (in the front corner near the power studs)

Got it pulled, thanks! I'll see what happens tomorrow on my way to work.

 

[The_Roadie]

Roadie... I don't suppose you happen to know the umber for the ABS fuse, and which box its in?

Yes, but it was a test to see if you would look it up in your Owner's Manual.

 

[Shdwdrgn]

Yes, but it was a test to see if you would look it up in your Owner's Manual.

Owner's what? Does not compute...

Unfortunately this did not resolve the problem. With the fuse pulled, the abs/brake dash lights stay on all the time, but did not start chiming like mad at me. However about half way to work it started shifting really hard again. I'm sure people look at me funny when I pull up to a stoplight, shut off my truck, and restart it.

I'm going to have a look through HPT today and see if I can turn up any options for disabling these tests. Maybe its defaulting to another table that I can modify temporarily. If anyone has any other suggestions to get me by, chime in...

 

[The_Roadie]

Pull the connectors for two sensors off the transfer case tailpiece? I never knew which of the two identical sensors was for the TCCM and which was used for the VSS.

 

[Sparky]

Hardtrailz has swapped gear ratios, but he also has a newer one which I believe is easier to reprogram for changes. I know you can program for tire changes in 2006, but not the 02-05. I would think you should be able to at least do an axle change reprogram on the older ones... Hm, maybe PCM4L could help you out there as they might know.

 

[Pittdawg]

I know my vehicle is newer but I simply reported the percentage off my speedo was to PCMofNC with my larger tires and 4.10's and they got it pretty damn spot on (as verified by my gps speed indicator on my smartphone).

 

[Shdwdrgn]

It occurs to me that from the recommendation I got off the HPT forum to adjust for the new gears, they also suggested changing the TCC shift/release settings. I just changed those tables back to stock, maybe I'll get lucky and this is where the problem lies? If that doesn't work on my way home, I can look for those sensors wires tonight.

PCM4less is a good suggestion. I was also thinking of checking with the local off-road shops and see if they knew of anyone who could reprogram for the gear change.

 

[Shdwdrgn]

Wow... I just had a dealership tell me they cannot reprogram gear changes, and I should check online for something like SuperChips to correct the problem.

 

[Sparky]

Wow... I just had a dealership tell me they cannot reprogram gear changes, and I should check online for something like SuperChips to correct the problem.

That might be a policy thing. 4 years ago I swapped the rear on my 98 Camaro to the optional rear and took it in for reprogramming. When they made the call to whatever dept they needed for the modified file they were told they were no longer allowed to do that for liability reasons. Totally took the tech at the dealer off guard because they used to do it all the time.

 

[Shdwdrgn]

OK here's another idea... If someone with HPTuners and 4.10 gears were to do a read-all and send me there file, apparently the changes I need are within that data (just not available to modify in the GUI), so maybe I can do a write-all to my PCM and have the corrections made? Then I just need to rewrite my VIN and custom changes back to the PCM and see if it works...

Anyone able to help out on this?

 

[HARDTRAILZ]

I did not have any issues driving around for a decent little bit with different gearing front and rear, but mine is the 06 and newer system. Had no funny shifting or lights at all. My speedo was slightly off after the rear went from 3.73 to 4.10, but once it was all together and matched I sent my PCM to be re-tuned by PCMforless and they re-did what I asked and updated my tire size and gearing and the speedo is accurate and the level three shifts are nice and firm without being rough.



--If you just rewrite to a 4.10 geared setup, you still will not be accurate on speedo due to the larger tires. There are charts that tell you what your effective gearing is. I would say you are closer to an effective 3.73 if you went 3.42 to 4.10 with larger tires.

With all the variables I believe my setup leaves me with about an effective 3.55 ratio if I was on stock tires.

 

[Shdwdrgn]

Previously, with my larger tires, my odometer was only off by about 2%. I did a 10-mile check against my odometer last night, and got a reading of 12.2 miles. Seems to me this means I'm off by 22%, even though I was expecting to be closer to 17% (19% for the gear change, minus 2% for the tire change).

I can live with things being off by 2%. I cannot live with a 22% difference, and apparently my computer can't either.

 

[kardain]

There is indeed an option on the GM Tech II tool to change the ratio. As you found, dealer's don't give it away. Anybody getting larger offroad tires is in the same boat, and EFILive and HPTuners have been attempted with less than total success to tune in the lower number of VSS pulses per mile that larger tires give you. As far as I know, nobody has been totally successful tuning in new tire sizes to adjust the speedometer perfectly.

Eric's the expert - let's see if he sees this thread to post a summary.

Uh, I successfully recal'd with HPT to accommodate a larger tire (no gear changes though). Granted, it's an 06 pcm, but speedo is 0.2mph slow at 75mph (0.1mph slow at 60mph) as compared to 7 different gps devices (well, smartphones/tablets from different manufacturers and different vintage all running GPS Status app). Police radar is dead on accurate... Don't ask

The variance is not enough to be a concern. If that's not considered a success, not sure what is.

 

[Shdwdrgn]

@kardain -- If we all had 06 or later vehicles, this wouldn't be a problem. But the 02-05 models are well known for not having easy options to correct speedometer differences.

 

[kardain]

@kardain -- If we all had 06 or later vehicles, this wouldn't be a problem. But the 02-05 models are well known for not having easy options to correct speedometer differences.

Very true.

 

[jimmyjam]

@kardain -- If we all had 06 or later vehicles, this wouldn't be a problem. But the 02-05 models are well known for not having easy options to correct speedometer differences.

Right, the problem is the P10 PCM
2002-2005 4.2L I6 - P10
2006-2007 4.2L I6 - P12
2008-2009 4.2L I6 - E67/T42

 

[Wooluf1952]

Mine has two off the rear driveshaft on the transfer case, one on the front driveshaft on the transfer case, and one on each front wheel hub.

See Roadies post below.

Pull the connectors for two sensors off the transfer case tailpiece? I never knew which of the two identical sensors was for the TCCM and which was used for the VSS.

 

[DJones]

See Roadies post below.

No idea what you're saying, they both detect speed, and have the same part numbers. Go figure.

 

[C-ya]

Wooluf quoted you and roadie for shadow.

 

[Wooluf1952]

No idea what you're saying, they both detect speed, and have the same part numbers. Go figure.

There are two identical sensors on the t-case tailpiece but only on is for the ABS. There is also one ABS sensor on each front wheel.

 

[Shdwdrgn]

I already posted this on the offroad site, but I've been playing with the programming the last couple days. I was told to reduce the TCC tables by 19%, but it looks like I actually needed to increase them. Made the swap this morning (and put the ABS fuse back in), had one more ABS warning on the way to work, but all was quiet on my way home. I think I finally have the right settings to limp by until I can get the system corrected for the new gears. The transmission is still pretty stiff on the 1->2 shift, but otherwise its running smooth. Doesn't seem worthwhile to try and adjust my tables until the gear correction is done, though.

Still hoping to find someone who can send me a full download from a PCM with the 4.10 gears. I haven't gotten any responses yet from any of the sites.

 

[Pittdawg]

I already posted this on the offroad site, but I've been playing with the programming the last couple days. I was told to reduce the TCC tables by 19%, but it looks like I actually needed to increase them. Made the swap this morning (and put the ABS fuse back in), had one more ABS warning on the way to work, but all was quiet on my way home. I think I finally have the right settings to limp by until I can get the system corrected for the new gears. The transmission is still pretty stiff on the 1->2 shift, but otherwise its running smooth. Doesn't seem worthwhile to try and adjust my tables until the gear correction is done, though.

Still hoping to find someone who can send me a full download from a PCM with the 4.10 gears. I haven't gotten any responses yet from any of the sites.

Your sig indicates you already have a pcmofnc tune. They will fix all of this for you for a nominal charge if you already paid them for your original tune.

 

[Shdwdrgn]

Actually I already wrote an email to Kelly explaining the gear change I was doing, and she wrote me back saying they can't correct my speedometer.

 

[HARDTRAILZ]

Your sig indicates you already have a pcmofnc tune. They will fix all of this for you for a nominal charge if you already paid them for your original tune.

Simply...NO. They can not. If you read that he has the 02-05 PCM, you would know it is not that simple.

 

[Sparky]

I knew they can't tune for tire size changes, but I wouldn't have thought that gear ratio changes was such a big deal.

Even then, I wouldn't have thought that a gear ratio change would make the ABS all angry either.

 

[limequat]

I've only done a few 02-05 tunes, but I've never seen a 4.10 calibration.
I think your best bet would be to go to car-part.com and order the PCM and the ABS module out of a 4.10 ratio truck.

 

[Pittdawg]

Simply...NO. They can not. If you read that he has the 02-05 PCM, you would know it is not that simple.

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