One of the curiosities of buying a classic car is that you suddenly become interested in the most arcane aspects of your beast’s welfare, and find yourself reading – and enjoying - stuff about your car that you wouldn’t dream of looking at if you weren’t an owner, much of it found in club and single-marque magazines.

That's how I came to be reading a ‘how to’ story on overhauling the front suspension of a Jaguar XJ-S, an example of which I bought last year. But the story that caught my eye in ‘Jaguar World’ was about vehicle diagnostic systems.

My XJ-S pre-dates today’s era of On-Board Diagnostic (OBD) sockets, but I know I’m not alone in worrying about the impossibility of carrying out any significant repairs to modern cars because they’re so stuffed with electronics. OBD sockets began appearing in 1996 for models sold in the US, and in all European cars from 2001 if they’re petrol and 2003 if they’re diesel.