Viano Immobilizer Problem Resolved

I own a Mercedes Vito, not sure about the build year, but I had a similar issue. The symptoms you describe sound very much like what I experienced with my vehicle. Did you try the spare key? Does the security light behave the same way with both keys? Was there any event that preceded this, such as a battery change or jump start?

Good shout with the spare key, I'll try that. But what exactly was the issue with your Vito then? Was it definitely the immobilizer?

Yes, in my case it was indeed the immobilizer. The key signal was not being correctly read. I would strongly recommend having the error memory read out by a professional. If it's the immobilizer, they will likely need to reprogram the key. Trying the spare is a good first step, but a workshop visit seems unavoidable in your case.

Thanks for the advice. Tried the spare, same thing. Took it to a workshop as you suggested. Turns out the key programming was indeed incorrect. They fixed it for 45€, which is a win. At least it wasn't an immobilizer bypass situation!