Interstar immobilizer issue

Sounds familiar. I had similar starting issues with my old Peugeot. The symptoms were identical; engine would briefly start and then cut out. The error codes pointed towards the immobilizer as well. It might be the key losing its signal, or a fault in the immobilizer module itself. Have you tried using a spare key, if you have one? That could rule out a faulty transponder chip in the key you're currently using.

Yes, I did try the spare key, and it's doing exactly the same thing. That points away from a dodgy key, or at least both keys being dodgy which I doubt. Where would you suggest I look next? Is there anything I can easily test before I have to admit defeat and hand it over to a mechanic?

Okay, if both keys are exhibiting the same behavior, it pretty much rules out a simple key issue. It's more likely a problem with the immobilizer system itself. Since you've already scanned for error codes, and it's showing an immobilizer fault, the next step usually involves more in-depth diagnostics. This is where things get a bit tricky without the right tools. There could be a wiring issue, a faulty immobilizer module, or even a problem with the ECU (Engine Control Unit) that's preventing it from authorising the engine to run. My opinion: the best thing to do is take it to someone with the proper diagnostic equipment. They can delve deeper into the car's electronics.

Thanks for the advice. Sounds like I was barking up the wrong tree. Bit the bullet and took it to a garage. Turns out the key needed re-programming, like I first thought, but it was a deeper issue than I could fix at home. Cost me 45€, but at least it's running again!