CLA Diesel Cylinder Pressure Fluctuation

Pressure fluctuation, eh? I had something similar happen with my CLA, though I can't say it's a dead ringer for your situation. Did you notice any weird noises or rough idling before the light came on? It could be a dodgy sensor throwing everything off. Have you hooked it up to a diagnostic tool to pull the error codes? That's usually the first step before tearing into things like piston rings, which, honestly, sounds a bit extreme at this point.

Yeah, I did use a diagnostic tool. It's throwing a code related to cylinder pressure imbalance, but nothing specific enough to pinpoint the exact cylinder or cause. No weird noises or rough idling, though. Just the reduced power and increased fuel consumption. That's why I'm thinking it might be something more fundamental than just a sensor. So your issue was similar even without those symptoms?

Okay, cylinder pressure imbalance... Hmm. Mine had similar symptoms, but it turned out to be a faulty sensor that messed up the readings and caused the error. It's tricky because a bad sensor can trigger a whole chain reaction of consequential errors. If you have the same, I'd say take it to a decent workshop and have them run a proper diagnostic with Mercedes-specific tools. Save yourself a headache before you start messing with things like head gasket or fuel injector.

Thanks for the insight. Turns out you were spot on. Took it to a shop, and it was a faulty sensor. They replaced it, cleared the codes, and everything's running smoothly now. Apparently, the sensor was causing a cascade of errors, just like you suspected. Repair cost was 0€ as it was covered by guarantee.