Ford G6 hissing sound and fuel consumption

Sounds like a vacuum leak, especially with the hissing. Check the intake manifold and all the vacuum hoses connected to it. Could be a leak near the turbocharger if your G6 has one. Get some leak detection spray and go to town – that'll pinpoint it.

Thanks! I can find the intake manifold, but which vacuum hoses should I focus on? And where should I spray the leak detection spray for best results?

Follow any small rubber hoses coming off the manifold, especially those towards the back of the engine. They crack with age. Spray around the hose connections first, then along the hose itself. If the engine sound changes when you spray a spot, that's your leak. For a proper fix and clearing that engine light, a workshop visit might be best.

Thanks so much! I followed your instructions, found the leaking intake hose, and had it replaced today at a local shop for 100€. The hissing is gone, and hopefully, fuel consumption will normalize. I appreciate the help!