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Is there a way to tell whether my car's ECU is factory original, or has been tuned by someone, like Kleemann or Renntech, or other? Reason I ask is, I have a 2003 SL55 AMG and the car has, I've been told, an aftermarket pulley on the supercharger. Those usually require a tune to the ECU? Not always though? This car is so fast, I am thinking it must have been upgraded, but I received nothing when I bought the car.
Case in point; About seven years earlier, I had a 2004 SL600 and one day, Kleemann was having a "summer sale" I guess business was slow, so they offered an ECU tune for around $600. I shipped them my ECU and when they received it, they called me to say, "You already have the RennTech tune in this, if we change anything you won't be happy, it's best just left the current state!" Kudos to the Kleemann people for being honest and knowledgeable. I contacted the guy I'd bought that car from and he said, "Oh, I didn't mention the RennTech tune cause I thought it might be a deal breaker"! LoL
So, today with my SL55, I've become curious as to exactly what may or may not haven been done to this car. It is really fantastic to drive. I'd like to know. Any ideas, thanks a lot!
Last edited by tonylinc; Nov 20, 2025 at 01:49 PM.
The ECU likely has a "Change counter", but that will be incremented even if the dealer applies an update or re-flash.
Not sure, but I suspect you cannot read the tune from the OBD2 connector; only write a new tune.
Reading a tune is generally a very technical process, requiring removing the ECU from the car and sometimes opening the case to directly access the chips. So basically, you would have to send the ECU to a tuner.
Maybe someone will correct me and/or other have methods of how to check if you have a tune.
A different way might be to use e.g. Draggy to perform some acceleration runs, such as 30-100 mph, and comparing them to owners with a known stock SL55AMG.
You don't need to send the ECU in for a M113K car. Most of the known tuners sell a OBD2 device that allows you to flash tunes / revisions, data log, etc.
If you have a reduced-diameter supercharger pulley and your car is running well, then chances are it has already been tuned.
Doubt it was tuned by RENNtech, though, since they never bothered with altering the supercharger pulley and instead focused on the crank pulley for their M113K upgrades.
You don't need to send the ECU in for a M113K car. Most of the known tuners sell a OBD2 device that allows you to flash tunes / revisions, data log, etc.
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Yes, all kinds of OBD2 devices can WRITE a new tune into the ECU and/or log all the typical data. They can also read basic info such as the VIN and software version number. However READING the engine tune is often more complicated; perhaps because manufacturers want to block that ability.
The SL55 AMG uses the Bosch 2.8.1 ECU. Various sources, includes the KTAG ECU programmer state that the only way to read the 2.8.1 tune is to open the ECU and connect it to pin 2 of the ECU main ROM. It also connects to various pins of the ECU's connector, but one critical signal line must go direct to the ROM. (I just did a read this week on a 2.7.1 ECU.)
I certainly defer to @HLG600 's experience that the reduced pulley likely means you have a tune. I'm just saying that to be absolutely sure would require sending the ECU to a tuning shop.
Thanks for the info, the SL55 is just as fast as my SL600 Renntech, so I figured it must have been turned somehow as well. The car really is something else. I don't think I want to take anything apart, for fear of breaking anything. LoL I'll probably just leave everything the way is is!
I have a Launch Creader V2.0 but I doubt that would shed any light.
Yes, all kinds of OBD2 devices can WRITE a new tune into the ECU and/or log all the typical data. They can also read basic info such as the VIN and software version number. However READING the engine tune is often more complicated; perhaps because manufacturers want to block that ability.
The SL55 AMG uses the Bosch 2.8.1 ECU. Various sources, includes the KTAG ECU programmer state that the only way to read the 2.8.1 tune is to open the ECU and connect it to pin 2 of the ECU main ROM. It also connects to various pins of the ECU's connector, but one critical signal line must go direct to the ROM. (I just did a read this week on a 2.7.1 ECU.)
I certainly defer to @HLG600 's experience that the reduced pulley likely means you have a tune. I'm just saying that to be absolutely sure would require sending the ECU to a tuning shop.
Agreed that getting into the specifics of the tune requires more advanced capability than just flashing, but if the OBD2 device can data log, then you can interpret the levels of boost recorded and compare to what factory is.
If the max PSI is beyond factory, you know you're tuned.
The alternative verification would be to find an "Autobahn" and gauge how far to the right you can send that speedometer needle.
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