My 355 passed its MOT this morning complete with my own left hand side Cat ECU module installed. I took it for a 100 mile drive later in the day and everything worked well. There were no bank shutdowns which is what was happening to me before I made this module.
I did see a brief flicker of the slow down light on one occasion, and will need to investigate that a little further. I expect this to be the MAX31855 IC returning unusual results, and if this is the case I can deal with it in the microprocessor code by adding plausibility checks and/or smoothing (for example if the temperature suddenly jumps by a large percentage, only accept the jump if several additional reads of the temperature still show that increase). I'll do some logging while on the move to verify what's going on anyway.
A good first test but a bit more work to do and this is exactly what I expected.
And a brief note on version 2 of the module: I received a bluetooth board in the post a couple of days ago. My intent is to get rid of the USB cable and make it possible to view the data on anything that is bluetooth enabled and has a terminal application available. I have yet to wire anything up but it should be relatively easy to do. It will be harder to fit the extra board in the OEM box though. I will report further on this a bit later.