XC40 Hissing Noise and Fuel Consumption

That sounds familiar. I have an XC40 too (though a bit older), and I had very similar symptoms last year. The hissing is a big clue. Have you checked for any obvious cracks or disconnections in the intake hose between the air filter box and the intake manifold?

Thanks for the quick reply! I did a quick visual inspection, but didn't spot anything obvious. Where exactly should I be looking on the intake hose? I'm not the most mechanically inclined, so any pointers would be great.

It can be tricky to spot, even with a good eye. Sometimes the cracks are small and on the underside of the hose. Given the hissing and check engine light, it's likely a significant leak. Prolonged driving with it will potentially cause engine misfire and other issues. To be safe, I recommend taking it to a trusted workshop and letting them do a proper diagnosis with a smoke test. It will probably be an intake hose leaking.

Okay, thanks for the advice! I was hoping it would be something simple I could fix myself, but it sounds like it's best left to the professionals. I'll book it in for a checkup. They indeed found a leak in the intake hose. Repair cost was about 100€. Thanks again!