Mercedes CLK reduced engine power possibly chip related

Reduced power and a stored error? Hmm, sounds like it could be related to that chip tuning. What diagnostic code did the scan tool pull up? Knowing that would help narrow things down significantly. Also, has the 'check engine' light come on? Has the fuel consumption changed? Has any other work been done to the car recently?

I'm not sure about the diagnostic code. Is there a way to be certain that the fault code and reduced power are related to the chip tuning?

Well, without knowing the exact diagnostic code it's tough to say for sure, but aftermarket chip tuning is a common cause for these kinds of issues on a Mercedes. Often, the car computer detects that something is outside of its programmed parameters and throws a code. The reduced power is the car's way of protecting itself. I'd suggest taking it to a reputable workshop that has experience with Mercedes vehicles and can properly diagnose the issue. It's likely they'll need to either re-flash the ECU with the original software or properly adjust the current tuning. Ignoring it could lead to more serious and expensive problems down the road!

Thanks for the insight. I took it to a workshop. Turns out you were right – faulty chip tuning by a third-party provider was the issue. The repair cost me 180€. Appreciate the help!