Well, somehow I seem to have fixed it, for the time being at least. I decided to have a last lunge at the problem before booking it into the garage again, starting with sparky Paul’s suggestion of banging the top of the dashboard. This didn’t work, but it made me feel so much better I didn’t want to stop.
Next I re-checked the battery terminals. A-ha! On the negative terminal the clamp nut was indeed nice and tight, but I spotted that that was because the clamp was completely closed on itself. Crucially, the clamp wasn’t tight on the terminal. The car has a replacement battery (Varta) and perhaps the terminals are very slightly narrower than those on the standard battery. The top of the clamp was level with the top of the terminal, so, as the terminals are slightly tapered, I gently tapped the clamp down to the base of the terminal, where I was able to tighten it properly.
That seems to have done the trick. I’ve cycled through all the various readout options and it’s still fine.
My thanks again to everyone who came up with suggestions - all very much appreciated.
Ric
