I imagine the immobiliser ring will work, but if it doesn't here are some of my experiences.
On my previous 3l Roadster the fuel pump relay failed. In typical MMC logic that relay powers the ECU. I thought I had an immobiliser issue.
Also the earths can corrode but it isn't always obvious. A clean might be in order. On my car I thought the starter motor was sticking but adding a jump lead as a makeshift second earth proved it was the engine to chassis earth.
