Slightly off topic, but you you mentioned fuse pulls in a Jeep...I'm a glutton for punishment and I've always driven a Jeep (though I do have a 4Runner for my reliable car) - learned to drive on a CJ.
Anyway, the head unit in my JK stopped turning off when I took the key out - so that was a fun battery-draining episode. I've been waiting for the weather to get nice to pull the head unit and put something else in there, so in the mean time I just pulled the fuse.
Of course the head unit is responsible for publishing outside temperature to the CAN. I don't care that the dashboard says --F instead of a temperature now, but on a cold start, the ECU doesn't know if the oil pressure is high because of a fault of just because the oil is cold. So if I get on the throttle even a little before the engine is warm, I get a CEL now. The joys of Jeep ownership.
I think those electronics are in the head unit mainly to provide interior weather resistance - just a feature other car designers don't generally need to worry about.
JK may have more CEL's than a CJ, but a lot more comfortable ;) but probably slower than the CJ
I’m extremely skeptical that the head unit pushes to the ECU.
To me, it sounds like you might have a faulty coolant thermostat. This part physically expands as engine temperatures increase. It’s essentially an analogue part.
It's the ambient temperature sensor, not the engine temperature sensor. My guess is that the head unit either contains the sensor or is responsible for broadcasting it. The head unit talks to the dashboard to redisplay nav instructions, I'm guessing it's also responsible for sending the temperature info to the dashboard. And since I pulled the fuse, all I get is --F, so the information isn't available on the CAN. Don't know why - I'm not an automotive engineer :)
Anyway, the head unit in my JK stopped turning off when I took the key out - so that was a fun battery-draining episode. I've been waiting for the weather to get nice to pull the head unit and put something else in there, so in the mean time I just pulled the fuse.
Of course the head unit is responsible for publishing outside temperature to the CAN. I don't care that the dashboard says --F instead of a temperature now, but on a cold start, the ECU doesn't know if the oil pressure is high because of a fault of just because the oil is cold. So if I get on the throttle even a little before the engine is warm, I get a CEL now. The joys of Jeep ownership.