Sprinter hissing sound and fuel consumption issues

I also own a Sprinter and encountered similar symptoms some time ago. The hissing noise, coupled with reduced fuel economy and the check engine light, does indeed suggest an air intake leak. Could you perhaps specify where you believe the hissing is originating from? Have you inspected the air intake hose between the air filter and the intake manifold?

Thanks for the quick reply. I haven't pinpointed the exact origin of the hissing yet, but it seems loudest on the passenger side of the engine bay. I've given the main intake hose a quick visual inspection, but didn't spot any obvious cracks. Is there a particular area of the air intake system that's prone to leaks on these engines?

Based on my experience, the corrugated section of the air intake hose, particularly near the turbocharger inlet, is a common failure point. The heat and vibration can cause it to crack. While a visual inspection might not reveal a small split, the hissing sound under load is a strong indicator. It is advisable to consult a qualified mechanic for a thorough diagnosis. A smoke test can effectively locate the leak. Ignoring it could lead to further issues with the engine management system.

Thanks for the advice. I took it to a workshop, and you were spot on. It was a cracked air intake hose, right where it connects to the turbocharger. New hose, fitted for 100€, and the Sprinter is back to normal. Fuel economy is back to where it should be, and the hissing is gone.