Seat Leon Hybrid No Start Issue

That's a frustrating problem. Intermittent starting issues can be a real pain to diagnose. Since it's a hybrid, have you checked the 12V battery connections? Sometimes a loose or corroded connection can cause all sorts of weird ECU issues and prevent the engine from starting. Does the check engine light come on at all?

Thanks for the quick reply. I haven't specifically checked the 12V battery connections myself. Where exactly should I be looking for corrosion or looseness? Is it just the main terminals, or are there other connections I should inspect?

I've seen similar things happen. The main terminals are the first place to look - make sure they're clean and tight. Also trace the cables from the battery, and check any grounding points you can find. Sometimes a bad ground can cause similar symptoms. If you're not comfortable doing that, it might be best to get it to a workshop. Intermittent electrical issues can be tricky, and if it's not the battery, it could be something more serious like a faulty sensor affecting the ECU or fuel injection.

The workshop confirmed your suspicion. It was indeed a poor battery cable connection. They cleaned and tightened everything, and the car is starting perfectly now. Total cost was 155€, much better than a full ECU replacement! Thanks for your help!