'99-'07 (Classic) Silverado/Sierra DTC C0238 + ABS Light, The Fix Thread

I figured i'd publish this fix for those that have swapped gears and/or tires in their Silverado/Sierra, and are getting ABS DTC C0238, and the dreaded ABS/Brake light and chime.

The issue arises when the gears are changed, or the tire size is changed enough to get outside of the allowed error percentage in the ABS system. These trucks do not have individual rear wheel speed sensors for the ABS system, rather it relies on the VSS signal produced by the PCM on the ABS VSS output pin, which is derived from the transmission output shaft speed sensor. This is why changing gears is usually the primary cause of this light, although going with larger than normal tires, or smaller will produce the same DTC if it's far enough out of the allowed threshold.

To my knowledge, there is only 1 way to properly fix this and do it right, which is the way i'm about to detail and the way that has been successful for me. Changing the ABS module's programmed tire size via a Tech 2 does not seem to be an effective fix in my experience either, as it's not the tire size that's causing the issue per-se, so much as the new gear offset. And, from what I understand, the Tech 2 only allows pre determined tire sizes to be programmed into it, you can't simply put the appropriate tire size you are running in there. This method, will make everything work like stock, with whatever size tire you have on the truck.

http://i1352.photobucket.com/albums/...pss6ntak6d.jpg
http://i1352.photobucket.com/albums/...pshowylsey.jpg

And here's what you will see that causes the problem in the ABS module setting the code. The front and rear wheel speeds are not in agreement, even though the tire size is the same:

http://i1352.photobucket.com/albums/...pslsq2vsjd.jpg


The subject vehicle:

2004 Silverado 1500
5.3L
34 in tires front/rear (advertised 35", but ALWAYS measure them!!!)
changed from 3.73 (stock) gears to 4.56

So, knowing this first off we calculate the basic's that we need in the tune. I personally, NEVER use the auto calculator for the trans tail rev/mile or vss output pulses/mile, it never seems to come out exact for me and that will cause an issue. However, it do keep it's values for the trans/TCC speed scheduling. Here are the values used on this truck:

Tire Circumference (Pi x Diameter) = 106.81415"
Tire Rev/mile (63360 - number of inches in a mile / Circumference) = 593.179836
Driveshaft rev/mile (Tire rev/mile -593.179836- x Gear Ratio - 4.56 -) =2704.9000
VSS Pulses/Mile (40 teeth on reluctor wheel for 4L60+80E x Driveshaft rev/mile -2704.9000) = 108196.00

Plug All of those numbers into the fields in the tune via HPT:

http://i1352.photobucket.com/albums/...ps5kbd3wer.jpg

Now, road test the vehicle and see how far off your rear wheel speed is. Depending on your setup and changes, it will most likely be a little, or a long ways off still. Next, you need to play with this box:

http://i1352.photobucket.com/albums/...psfhcrcwl1.jpg

You see, the ABS Module expects 128k pulses/mile to get that rear wheel speed. Changing this value, will change the rear wheel speed reading. It's now as simple as moving the value UP or DOWN (Making the number larger will SLOW DOWN the MPH in the ABS module for the rear wheels, making the number SMALLER will speed it up) and re-logging the speed signal in the ABS, until they match, like this:

http://i1352.photobucket.com/albums/...psexxusf2g.jpg

No more ABS Light, no more annoying chime. The ONLY stipulation to this will be that you have to run the calculations BEFORE you do your gears/tires, just to make sure the values you need to put in the boxes, don't exceed their maximum value. IF that case does arise, grab a signal conversion module such as the Dakota Digital SGI-5 box, install it in the transmission output shaft speed sensor signal circuit, and do the math on the stepped down pulses.

The value I ended up on this truck was 113,000 on the ABS Pulses/mile to get the rear wheel speed to agree, your results may be different. ALWAYS, ALWAYS, ALWAYS Measure the height, OR perform a roll-out check to get that circumference. Just because a tire is advertised a certain diameter, does NOT mean it measures as such, and that will adversely affect the results of this. Once all this is done, finish out by correcting the speedometer by adjusting the General VSS Pulses/Mile count (remember, ADD MORE to the value to slow down the needle, SUBTRACT to speed it up). Most stock vehicles I have to adjust about 2-4,000 pulses/mile to get the speedo dead on.

That's my solution, and has been working for a few years now.

I appreciate any input or further advice from people who have had this concern and their fix as well. I'm sure there are more than one way to kill this issue, but for me, this seems to have been the most effective, with no dealer level programming of the ABS system.

Dang this will be a big help. Just got an 05 truck that has 35" tires and potentially a gear change as well, not sure, but right now the speedo is WAY off reading like 20-30 mph faster than I am actually going. Hopefully with some calculations I can try to dial this in. Bad part is I have no clue on the gears as the guy I bought it from was likely just a flipper.

Absolutely! You will have no issue getting your speedometer dead on with these instructions. Typically, I've found that after calculating all of the values manually and putting the numbers in the appropriate box, that the stock speedo is biased fast by about 2-3 mph. This is typical among auto manufacturers, so that it keeps the average consumer out of trouble with speeding. They are almost always baised to read faster than you are actually going. I usually have to adjust the General VSS Pulses/Mile 2-4000 pulses more than I manually calculate to get the needle dead on with GPS.

Does this require a complete write/flash or can you just write changes?

It's write changes only procedure, no entire re-write necessary. You will, however, need an aftermarket scan tool to access and view the ABS's wheel speed data as you calibrate the ABS Pulses/Mile setting, so that you can make sure they agree as I have demonstrated here, in the pics with the Red colored scanner.

I use a Snap-On Solus, which seems to work fine for all my needs.

Hmm, that might be interesting. Dont have any scanner other than hptuners.

Well took a little figuring to get the gear without pulling the cover, but it seems I have 4.88 gears in the truck. Basic procedure for those that need to know in the future, jack up the rear end, have truck in neutral with supports and wheel chocks, put tape on the tire and driveshaft, spin the tire 10x and count how many times the driveshaft turns. Since the g80 is a locker, it probably will not be locking and will act open. If one wheel stays stationary while you are spinning the other tire while transmission is in neutral then you will need to take the number you arrive at for the driveshaft and double it, then divide by 10. For me, I got 24 and a fraction turns. Double this and divide by 10 and you get 4.8x. Since the most common gear size in this range is 4.88, I figured that was the gear size. Punching that and the 35" tire size got me within a mph our two of GPS. The ABS also seemed happy after these changes. I believe the gears were the main issue.

Bringing this back from the death. Will this procedure appeace my traction control. The vehicle is an 01 tahoe stock. It has 24" wheels and i tried to correct the speedo using the hpt calculator for tire size. The speedo is now dead on but if u go past 20 the traction light will come on and i get a dead pedal until i stop. The only work around i found is to drive with the traction off. Will this method work on my issue?

It should, couldn't hurt to try.

Is there a consistent way to manually calculate the ideal value (value required to get rid of C0238 DTC) of "VSS Output Pulses per Mile - ABS" without needing the Snap-On Solus?

In the above example, for "VSS Output Pulses per Mile - ABS", we've gone from the stock 128,000 value to 113,000 for a reduction of 15,000 or 88.28% of the original 128,000 value. The value of 2704.9 for "Trans Revolutions per Mile" appears to have been increased from the stock value of 2537.988 (if my repository research is correct). An increase of about 93.83% (which could be close enough?)

Am I correct in thinking that the "VSS Output Pulses per Mile - ABS" value must be adjusted inversely of the modified "Trans Revolutions per Mile" value in order to get rid of the C0238 DTC? If the transmission rotates faster than stock, then the ABS will be receiving too many pulses per mile? And vice versa?

This is my first post here and I'm asking because I just bought the MPVI2 mainly to get rid of the Brake and ABS lights that come with C0238 DTC. It is driving me bananas. I had a mechanic verify that the front wheel speed sensors are working. C0238 is the only DTC I am getting since changing tires/ rear gears.

Vehicle is 2000 Silverado 6.0/ 4L80e. The stock configuration was 29.62" tire diameter and 4.10 gears; I've changed it to 35.25" tire diameter (37s with rollout circ of 110.75") and 4.88 gears. This changes my (General) VSS Pulses per Mile to 111674 (was 111684 stock. Very close to stock!) and the Trans Revolutions/Mile to 2791.8447 (was 2789.999 stock) which is 99% of original. The speedo is correct (indicated vs. GPS has the same error as stock; indicated is about 1-2mph faster than GPS which I'm ok with for now). The strange part is that if I enter the new tire size and gear in the wizard, it gives me 111682 and 2792.0506!

It seems like I should be able to leave the "VSS Output Pulses per Mile - ABS" value as is since the "Trans Revolutions per Mile" value is so close to stock. Would I really need to adjust it 1%? Anyone successfully do this with 37s and 4.88s?

I've strained my last brain cell to write the above, my brain is on fire! I need help from someone smart!

There may indeed be a way to work it out mathematically, however I never put the time into doing so when I developed this fix. I have fixed many trucks this way, but never used any other method other than using a scanner capable of communicating with and reading the ABS module's indicated wheel speeds. This will display the front and wheel speeds, and what you will find is that the rear wheel speed will be skewed vs. the front's. Make them match by changing the values in HP Tuners under the Speedo>ABS pulses/mile box. It takes a few guess and checks, but once you get the speeds to match in the ABS, everything will work just fine :). If you have someone that has already verified your front sensors are working (which they will be, the code will send you down that path when in fact it's the gear change and inferred rear wheel speed reading causing the issue), he surely had a scanner that could see the abs module and view those sensor input values, which is all you need. About 10 minutes with that scanner,and some highway driving will get it all fixed up :).

OK cool thanks! I'll have to use this method then.

I appreciate the help!

Ha yall should get a chuckle: I ran the stock settings for the first time with the bigger tires and 4.88 gear this morning and it worked perfectly! Speedo within 1 mph of GPS, shifted fine, and most importantly NO C0238!

Just assumed that it would need to be changed so never tried stock settings. I shouldve known when the calcs came out so close to stock. I already had a hypertech tune on it when I installed the tires and gears.

So for future reference, 2000 Silverado 2500 HD with 37s (110.75" rollout circ.) and 4.88s should work fine with no changes if the truck came with 4.10s.

Surprisingly enough my 2002 works almost stock when it came with 3.73 and I went to 4.88 and a 35 inch tire as well.