Ever since correcting the speedo on a 08 Silverado for taller tires, the ABS Inop and Brake Light have been coming on. Tire size went from 30.7 to 33.2. After doing some digging around, it looks like maybe the ABS Module needs to also be programmed with the new tire size with a Tech 2. Does this sound right? If so, can a Tech 2 program for any tire size or only one that was offered as a factory option?
I have a NBS chevy with 35's and I have the same problem. You used to be able to go to gm and have them recalibrate the ebcm for the tire change. Well I took mine to the dealer and the tech 2 could not make the changes on the NBS EBCM. It sucks. He said GM might come up with an option to buy a whole new ebcm with a different tire size. It is BS as far as I am concerned. Just wanted to let you know that you are not alone.
Can you guys post your before & after tunes?
We might be able to fix it.
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here is my stock tune and my current tune. Thanks for taking a look EC.
Another thing I don't understand is on the stock file under Speedo>Current Gear Ratio it showed 3.73 and this truck came with 4.10 gears.
2xLS1 - Yeah I don't understand GM's logic with the 4.10 in the Ratio slot and 3.73 in the Gear slot.
My guess here is to take put the stock VSS revs/dist values back in and change the General VSS Pulse/Rev value so that your speedo reads correctly. Then adjust the shift points accordingly. That might keep the ABS goonies at bay. The ABS does a compare of the front tire speed to the trans output shaft speed. As long as the front to rear relationship is maintained the ABS system is happy.
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should the values for "vss tire revs per" all be the same. The stock values are the same dist and dist-trans (650) but the dist-err value is 65. When I do a tire and gear change, all of these values are the same. Thanks for your help EC. I am thinking of changing my new dist-err value (580) to 58 and see what happens. It is worth a shot as a new EBCM from GM is not going to be cheap.
I looked into the ebcm thing as well. I'm a gm tech and in the past when you installed a new ebcm you had to set up the tire size amoung a few other things.
I was correcting the speedo in a nnbs 08 diesel the other day and thought I'd be a superhero and do the ebcm as well, no option for that anymore. The Older stuff (06 and older) still seems to have that available onthe tech 2.
I'm assuming that the general has incorporated all the ebcm settings on the tis website where you just download to the vehicle via a passthrough connection according to VIN number. Basicly if they didn't build it that way, those options, those tires, etc you are SOL.
On the other side of the coin as long as you are under 15% difference in speed from the pcm output/front speed sensors it doesn't seem to set a code for the abs, etc. At least so far so good for me anyway.
The whole point of my rambling is that a new ebcm wouldn't help you anyway, at least I don't see how it would.
Tony
^^^ Correct. The EBCM is looking at the trans output speed for ABS controls as it's actually 3-wheel antilock not truly four wheel antilock.
If the rear end had wheel speed sensors instead of the trans output being used for ABS functions there would be no problem as the tire size would be the same and the ABS output would be the same.
It's a problem with no direct solution. You can try messing with the VSS pulses/rev value but that's a bandaid not a fix.
The EBCM/ABS needs to be altered for a correct fix. Probably not ever going to happen with the liability issues that would create...
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was this problem resolved?
I thought this might interest somebody. I loaded a superchips tune with the adjusted tire size and gear ratio on my truck and read it with hptuners. I copied my current tune to the superchips file but left their speedo correction alone. The values under speedo are all the same except the general vss pulses per mile. When Superchips does the speedo correction I get a ppm value of 128458 and I also get NO ABS light or parking brake light. With Hptuners, my ppm value was 103585 and I was getting the abs and parking brake light on everytime I drove the car. Anyhow, I found this quite interesting. I have had the larger value in for ppm and I have yet to hear the dreaded chime.
Did a 07 today w/35" tires & 4.56 Ring & pinion.
Had the same issue with the ABS light.I raised the PPM about 20000 more.It cured it.
Thanks
For the info.
Might be a good idea for a sticky or something.
Just programmed another 08 with a 32.5" tire size and had the same problem. Is there some reason HPT can't make this work right? I was told that the err parameter needs to stay set to 1. If that is true, why does HPT change it? And I'm not seeing any ppm parameter in the NBS trucks. This truck had the Dist Err set at 67.62 on the stock file. Every other 08 file I have has it set to 6xx.xx the same as the VSS Tire Revs Per. Why was this one so low.
Last edited by 2xLS1; 07-12-2010 at 12:42 PM.
Email support the .hpt file in question, your serial number & a link to this thread and we can double check the address but its likely just GM fudging their numbers to get things to work right.
It doesn't have to be perfect, it just needs to be done in two weeks...
A wise man once said "google it"
FYI just to keep this public record the setting/address were correct, gm likely has a scalar of 10 in there somewhere.Originally Posted by 2xLS1
It doesn't have to be perfect, it just needs to be done in two weeks...
A wise man once said "google it"
Then why does HPT change it when you apply a new tire size. This is the part I'm saying needs to be fixed. Take that stock file and change the tire size to 32.5 and commit. If there is a x10 scaler why does HPT change the Dist Error from 67.62 to 620.55 and change the Err from 1 to 3.73. Like I said, I've been told that the Err value needs to stay set to 1.
To fix the problem I set the tire size to 32.0 and set the Dist Err back to 67.62 and the Brake and ABS lights went out. I don't know what change fixed it because I changed both on the same flash.
In that case you'll likely need to manually scale the values, gm probably used some oddball way to calculate gear/tire for that application as compared to the other similar operating systems, wouldn't be the first time and won't be the last time.
It doesn't have to be perfect, it just needs to be done in two weeks...
A wise man once said "google it"
HPT is scaling right, but they are sticking the new "Dist - Trans" scalar value into the "Dist" and "Dist - Err" scalars, for what reason I can't understand. It's simple, all you do is get the ratio difference between the old/new tires (or axle) and then just scale the values in those 3 particular parameters by that difference.
Last edited by RWTD; 09-28-2010 at 09:04 PM.
Formerly known as RWTD
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so was there any real positive solution to this because i just did my brothers 08 silverado that has 34.5 inch tires and its doing the same thing.
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I don't understand why you guys are having problems?! I've never had a problem adjusting tire of gear sizes in the speedo>general tab.
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