Twingo check engine light vacuum leak

I've got a Twingo too, and I had something similar happen. Check the hose connection from the pump to the valve. Mine was cracked and causing a vacuum leak. Is your idle rough at all?

Where exactly is that hose located? And how would I know if the idle is rough? It sounds normal to me. What does it mean if the idle is rough?

It's near the throttle body, follow the vacuum hoses from the manifold. A rough idle would be when the engine RPMs are unstable when the car is sitting still. If you're not sure, just take it to a workshop. A mechanic will spot it right away. It could also cause manifold pressure issues.

You were spot on! The mechanic found a defective hose connection from the pump to the valve. They replaced it, and the check engine light is gone! Cost me 175€, but worth it for the peace of mind. Thanks for the help!