pscan.uk

I think that you do, and I think that it's broken That's what the error code means.

On your dashboard instruments you have a warning light to tell you if the engine is too hot. The error code is telling you that there is something wrong with the warning light. If the engine becomes too hot, you will not see a warning light.

I have customers who are using newer versions of MAC OS (but only with Intel Macbooks).
The problem is that I cannot officially support it because my Macbook Pro is too old (it's an 8,3) so if you have a problem then I would struggle to replicate it.
You can download the software and try it before purchasing an interface. It won't communicate with a vehicle but you can at least see if the software installs and runs.
Also there is a thread here https://www.the-t-bar.com/forum/pscan-uk-diagnostic-tool-forum/97915-mac-osx-compatibility

Rob, please can you download the test program mentioned above and run it on the machine that has Citrix on it and send me the output.

Until I figure that out, please open a terminal window and type the following commands:-

cd pscan.uk
./pscanloader

Are any 800 owners able to assist? I only have an ECU, not an actual car.

Last week I had travel to assist my wife with some stuff relating to her family and I next week I am travelling for work. However I do have stock of pscan units and they are available for purchase.

If it works please reply back as confirmation would be useful.

pscan does not yet support coding in Rover 75 fobs.

pscan will work fine on old laptops.
If you can manage it then I would recommend a lightweight Linux such as xubuntu.
Personally I use an old Lenovo T420s, and I also use old Dell D620 and D630s, but just avoid the ones with Nvidia graphics (the ones with Intel graphics are fine).
Mucking about in the garage is a kind of harsh environment; it is so easy to trip over a cable or drop it on the floor, and I think a dedicated cheap old laptop is the way to go.