Seat Ateca Immobilizer Issue

Sounds like a classic immobilizer fault. The brief start and then immediate stall is a common symptom. Does the error memory specify anything more specific than just an immobilizer fault? Have you tried your spare key, if you have one? It would help rule out a general car electronics issue versus a specific key signal problem.

The error code is somewhat generic, pointing only to a general malfunction in the anti-theft system. I have not tried my spare key yet. If the spare key works, does that definitively indicate an issue with the primary key's transponder, or could it still be a problem with the ignition control module itself?

If the spare key works, it's highly probable that the issue lies solely with the primary key. While a faulty ignition control module could theoretically cause similar symptoms, the fact that a different key resolves the issue strongly suggests a problem specific to the original key's transponder. Recoding or replacing the problematic key would be the logical next step. I'd advise taking it to a workshop specializing in car electronics and security systems.

I took it to a workshop specializing in car electronics. The key's programming was the culprit. They recoded the key, and the anti-theft system now recognizes it. Total cost was 45€, a relief compared to a full immobilizer replacement. Thanks for pointing me in the right direction!