Seat Alhambra Excessive Fuel Consumption and Hissing Sound

That sounds familiar. I had a similar issue with my Alhambra, check engine light and everything. Have you checked the vacuum hoses, especially the one connected to the turbocharger? A leak there can cause those symptoms, including the hissing sound. It may also cause an engine misfire. Does the engine idle smoothly, or does it seem rough? Have you noticed any difference in the car's performance besides the fuel consumption?

Thanks for the quick reply! I did a quick visual inspection but didn't see anything obvious. Where exactly should I be looking for this vacuum hose? Is it easy to get to? If it is leaking, would I be able to feel it or do I need some kind of leak detection kit?

Yes, it is likely the vacuum hose I mentioned. Without specific tools, it is hard to pinpoint the exact location of the leak, but often, a visual inspection and feeling around the hoses can reveal cracks, especially near connection points. Given the symptoms and the check engine light, it really does sound like a vacuum leak affecting the turbocharger. You could try spraying some soapy water around the hoses while the engine is running and look for bubbles, but honestly, I would suggest having a professional mechanic take a look. They will have the proper equipment for leak detection and can diagnose the problem accurately. It should be a relatively inexpensive fix if it is just a vacuum hose.

You were right! The shop found a cracked vacuum hose near the turbocharger. They installed a new hose, the check engine light is off, and the hissing is gone! Fuel consumption seems normal again. Total cost was just under 100€, so thanks for the help!