OBD2 won't sync with my C3

I just bought my second C3 after covering 200,000 trouble free miles in my first. My latest one is a 1.1 petrol (the first being a 1.4hdi), and was manufactured in 2004.
The car ran fine for a couple of days, but out of the blue, it started losing power, and the engine warning light came on. Initially, I thought it could be a dirty lamda sensor, as I had poured some injector cleaner in before setting off. So I tried an "Italian service" (3rd gear at 70) to try and clear any carbon buildup. This didn't help. The problem comes and goes. I have noticed however, that switching the engine off, then restarting brings the power back, but doesn't cancel the light. This is a pain in the posterior end if I have traffic behind me, and I have to be careful not to engage the steering lock as I do it.

I bought a scanner to hook up to the OBD2 socket in order to diagnose the problem. The screen on the scanner lights up, and says hello etc. But it will not sync with the car. The scanner was cheap, but it had very good reviews. It also states in the handbook that it works with Citroën cars.

Any advice would be much appreciated.

Hello RobBlaenauFfestiniog

Early C3s aren't CAN-Bus (and are not OBD2 compliant), I think it's likely your scanner can't deal with VAN-Bus, Citroen's in-house protocol. Some scanners can read general parameters from the early C3 but often with ambiguity and errors.

If you want to read the C3 properly you need Lexia (or a Lexia Clone) which is Citoroen's dedicated reader.

There's loads of information on this forum about Lexia, just give search a go