DS4 engine start failure

That sounds frustrating! I had a similar issue with my DS4. Does the engine crank? Or is it completely dead? Have you tried your spare key? It might help narrow down if the problem is the key or something in the anti-theft system.

Yes, the engine cranks, but won't stay running. The spare key does the same thing. Could it be the key programming?

If the spare key does the same, it points to a key programming issue, or a fault in the immobilizer. I took mine to a workshop. They diagnosed and reprogrammed the key. Best to have it checked by a professional.

I took it to a workshop as you suggested. The key needed reprogramming. The repair cost 45€. Thanks for pointing me in the right direction!