This is the exact dongle that I use. It works with BimmerCode and Car Scanner. I haven’t had any issues with it at all. I’ve used it in the fashion you’re hoping to use it in too (real time stats), without issue.

In regards to your question about the thermostat and ECU, I’d have to say no. That doesn’t sound like an issue with the ECU. If we just game this out using standard logic we can pretty much prove it doesn’t have anything to do with the ECU. So the values for various variables which are either a part of functions or passed to functions as arguments/parameters are part of the software running on the ECU. For the thermostat and fan it would be something sort of like … (sorry for the atrocious formatting and shitty pseudocode, I’m on my phone).

def run_tstat_fan(is_fan_running=0, tstat_temp=220): if not is_fan_running and tstat_temp >= 219: run_fan() else: Log = write(Exception.e())`

So since the variable that determines at which point the fan should be turned on (the variable that’s set to 219) is hard coded in the ECU (and remember, manufacturers never intended for these values to be altered. Tools like BimmerCode change these sorts of values but it’s basically hacking the ECU, and it’s not intended behavior.) it wouldn’t be possible for the ECU to just randomly change this value to a different one which would result in the fan turning on at a different temperature. So that is definitely not what it going on.

Now depending on what year your car is, and how much of it has be switched over to digital systems VS stuff like relays, it’s possible some other stuff is going on and this is just the easiest way they could explain the situation to you. Long story short, it’s most likely an issue with the relay that controls the fan. They’re super cheap and they’re easy to replace. If your car has one (it probably does unless it’s like brand new but even then it may have one too) you should just try replacing it and see if that fixes the issue.

Finally, I guess technically it could be the ECU but it would need to be corrupted and it’s likely there would be other ECU related issues too. The chance of it being an ECU issue and having the only part of memory impacted be the variable that store the fan temp turn on value, and that the value is a readable one and a good one that’s usable, etc., is infinitely small.

Sorry if this is sort of rambling and not super well written but I’m on my phone and trying to get some other stuff done at the same time.

Edit - just to be clear… when the example code I gave would run on the ECU the ECU would then raise the voltage on the pin that’s associated with the relay for the fan. This would engage the electromagnet in the relay and that would complete the circuit that gives voltage to the fan itself so that the fan turns on. Just wanted to explain that part so you had a better idea of how it worked.

OK, looking through the OBD devices, is there one you recommend? These are new to me so I'm not sure which to go with.

Edit: just watched a YouTube vid and they had this one as a recommendation. Amazon will have it to me same day. Thanks so much for letting me know about this!