I think I'll grab one of the Anritsus from work and have a sniff around.

That'll do it, although is probably a bit overkill. One of these would do nicely https://eleshop.eu/rf-explorer-wsub1g.html. Some bright spark thought they would be useful for us but got this one https://www.amazon.co.uk/Spectrum-Analyser-RF-Explorer-Combo-silver/dp/B00ENEH2KA. Cheap n cheerful but works although totally surplus as we've all got one of these https://www.keysight.com/en/pdx-x201902-pn-N9915A/fieldfox-handheld-microwave-analyzer-9-ghz?cc=GB&lc=eng in the back of the van

We have also since seen spurious RF transmissions corrupt settings within the BECM too. So it is feasible yours may have temporarily inhibited it from sending through the correct code (or any code) to the GEMS ECU.

Be interesting to see what you find.

Gilbertd wrote:

That'll do it, although is probably a bit overkill. One of these would do nicely https://eleshop.eu/rf-explorer-wsub1g.html.

Yeah, but I'd have to buy that, rather than recover it from a dusty corner of the workshop store ;-)