realien

hi guys,

I posted here on an issue I'm having with the rear differential -

The dealer updated the software, cleared the codes in the TCU and checked the wiring to the differential and found no issues other than some stored codes around differences in wheel speed, which they cleared. I now get the warning every day, within 60 seconds of driving.

I'm wondering if anyone else has a different tire ratio and seeing an issue, I find it hard to believe such a small change could cause this.

My tires are 305/30/20 and stock is 295/30/20 - its about a 1% impact on revolutions per mile based on this

I'm not due for new tires yet, if I was I'd try it and see the problem goes away, but I'm skeptical.

Anyone else running a different tire ratio seeing this issue, or not ?

kumizi

Shouldn't be the tires. I'm running 315/30/20.

Do you have a code reader? Buy a cheap one off Amazon and pull the codes. Might find an answer that way.

Skilly

Im running 325/25/21 and no issues. Something else is playing out there.

kumizi

Do you know your build date? I know there was a driveshaft recall on some 2016 GTS models. Just spitballing. Dunno if a driveshaft problem would lead to a differential related message.

realien

They ran my VIN through MB's systems and the only thing was a software module campaign update. No Recall.

realien

I have one, no codes, MB themselves pulled a code from the trans that showed a speed difference in one of the wheel sensors. It doesn't through a CEL, just a stored code. I used the MBII which is better than a typical ODBII reader and it read nothing from the Transmission computer.

realien

I asked if there could be anything else, the AMG GTs tech insists it could be due to my 305/30/20 tires and if I want to confirm it's 3 hrs of diag at $195 an hour. So I guess I'm going to wait until I need to replace the tires, do regular 295/30/20's and see if it goes away.

I'm very skeptical that it's tires.. but I'm not an AMG GTS tech.

Keon

There's no way that its your tires. A 10mm increase in width is the equivalent of having low tire pressure, so MB would have accounted for that when building the transaxle. I'd try another dealership.

realien

thanks mate, I've booked at another dealership for Monday, we'll see what they think.

BBS63

If I am not mistaken all wheel speeds are recorded thru the ABS wheel speed sensors and the trans output speed sensor and then fed to various control modules like the ABS module which works with and sends the data to the ESP Module and other modules in the various ECM components.
I dont think tires size has anything to do with your issue, sounds to me like a reading error or the interpertation of the data being sent/received. I have learned in my short time owning a GTS, there is a module for everything !!
Good luck,

realien

yeah I asked if a wheel speed sensor could be at fault or a fault in the module, they did find faults in the module, updated the software and cleared the faults. But they didn't say anything about the wheel sensors, i asked if that could be faulty and they said there was no codes (although the module said there was a wheel speed difference between the two weehsl). They were a bit high and mighty about the tech's opinion on tire size, which tbh turned me off, I'm not an AMG Tech but I am a car guy, I've changed clutches, transmissions, turbos, heads, timing belts, etc, I'm not an un-educated consumer and I would have liked more suggestions rather than only one idea that seems implausible.

BBS63

I hear you, most Benz dealers tend to stand behind the curtain "oh well its not factory this or that. so thats got to be the problem" Ran into that years ago ahen i had my G55 and had spacers and had a shimmy in the front end and they immediately went with the "well he has spacers" so i took them off and took it back, to which only did they find it was the gear box was the issue. Lucky for me i have known the same SA and tech for years so they are real good with actually dealing with the issue first and not putting the blame on what I have added to the car.
Wish you were closer to me so we could swap wheels and tires so you can tell them, lookie lookie OEM wheels and tires.... same code now what.

From what I can tell, your problem started when after a rain so I am willing to put blame on a module or harness issue.
Keep us informed, you will get it sorted out.

realien

Thanks, yeah since the updated the software its worse, I get it every time I drive within 30 seconds, used to get it once a week after rain

realien

Dropped it off this morning at RMB Atlanta, hopefully they some new ideas.

realien

So after going to the new dealer, they didn't have a standard diagnostic procedure for this particular error.

MB central asked them to actually measure the circumference of the tire. Turns out even though both tires say 305/30/20, ONE tire is 1/4" larger in circumference than the other tire. I bought the car used, otherwise, I'd be going to the tire shop asking which tire factory has no quality control.

So, going to have them put some new PS4's on the rear, we'll see how that works and if it fixes the issue.. that's just crazy, 3 shops and 4 months later... I would never have thought to literally measure the circumference of the tire..

kumizi

That's wild. Would be awesome if that fixes it.

Which tires are you running right now that are off by that much in the same size?

Skilly

That would be shocking if it fixes it - simple day to day operations like turning a corner would great much more differential in travel distance than 1/4" circumference between the rear tires.

realien

Don't call me out, they came with the car . It has Khumos on it right now. I'm replacing them with PS4's today.

realien

will be interesting to see, MB themselves told the tech that they have seen this issue before on circumference differences. Guess I'll know more today when they clear the code and test drive. TBH it wound't surprise me, these cars are very picky about what they read over the sensors to make repair more of a replace than diagnose.

realien

So if this doesn't fix the issue, they'd recommend replacing the trans and diff. It's not under warranty. I think I'll go throw up.

kumizi

Is the car operating fine? Just the message on the display?

realien

The car runs and drives fine, the diff just doesn't lock. so in a corner you can feel it when its not locked. It used to happen sometimes. so in a corner it was tight, when the error comes up it feels loses, I guess because the diff is open. Its not affecting me day 2 day, but would affect me on the track, and of course re-sale.

realien

Did some research on this. There is a speed sensor on the clutches inside the transmission. It was a common failure on the Ferrari California that uses the same transmission and dealerships replaced the trans, indie shops replaced the speed sensor, its about $8k at typical exotic car shop rates. The difference here is that generally when that speed sensor fails you lose either even or odd gears, I have not had this issue its more of a warning.

BBS63

Well aint this some s**t ! Tire circumference bigger by a quarter inch? And MB Central says if that doesnt fix the problem than its the Diff/Tranny? This just gets wackier and wackier.
What if that doesnt fix it? New engine and wiring harness?

This is weird, you drove the car for how long with this one tire being bigger? And the code came up during a rain period, correct? And they 'updated" the module and since then no change.
Sorry for all the questions, this is just mind boggling when they start saying well if it aint the tire then its the diff and tranny.

realien

I think the issue is modern dealerships don't diagnose problems, they replace parts until the problem goes away. Mercedes doesn't even sell the parts for the transmission, they get the whole unit, so indy shops have created relationships directly with the suppliers to get parts.

I guess if it got a new transmission and that didn't fix it, they'd recommend new doors and a new hood

I got the car back yesterday with new tires, no issues so far, it will usually show up 100 miles after clearing the codes so we'll see if the new tires fixed it.