Mercedes E Klasse Hybrid Air Intake Leak Suspected

Whoa, that sounds familiar! I drive an E Klasse too, and I had almost the exact same symptoms: the hissing, the check engine light throwing codes, and my fuel economy tanked! It was driving me nuts. It turned out to be a cracked air intake hose. Really check those hoses, especially the ones connected to the turbocharger. Is the hissing louder when the engine is cold?

Can you provide specifics regarding the hose location and whether you observed any visible damage prior to diagnosis? Also, did you experience any engine misfires?

Okay, so mine was the main intake hose running from the air filter box to the turbo. I couldn't see the crack at first, because it was on the underside. You might need to feel around. And no, I didn't get any noticeable engine misfires, just the other stuff I mentioned. Honestly, if you're not sure, best take it to a mechanic. It could be something else, and you don't want to mess with the turbocharger. I hope you will get it fixed soon!

Acknowledged. I appreciate the insights. I will proceed with a professional inspection and repair. The projected cost is approximately 100€ for the hose replacement.