[Arragonis]

One immediate thought that occurred reading this was a loose connection in the OBD port but then again it is digital so you would get the right signal or nothing. On my car the port is completely closed when a cubby hole door is shut so I had it going off a couple of times when the plug was nudged out.

So (another theory I'm afraid) could it be a faulty temp sensor on the engine occasionally reading very high ? That would lead to the SG2 'sampling' that value and occasionally displaying it.

You don't get a warning because the ECU is programmed to smooth those things out before reporting a fault. i.e. the ECU designers realised that physical components occasionally go wrong and they compensated for it in software.

You could ignore it or get the sensor changed - start with the cheapest bit.