05 TL, 195k miles, recently passenger compartment heater not working or getting hot, also within recent past radiator fan seemed to be sporadically running after ignition turned off, to top it off engine light lit on dashboard; do not want to put massive amount of $$ into fix but would at least like to explore options and underlying reasons for symptoms, thx

 

Get the CEL run to see what code it is throwing a report back.

 

Also try searching for heating / ac self test. It will show you the code on the display without any readers.

 

OP, any of the auto parts stores will read your codes for free.

As far as no heat in the cabin, it could likely be the heater control valve. They are known to go bad:

https://acurazine.com/forums/third-g...ve-diy-747304/

 

Heater control valve gets stuck sometimes. Try cycling the AC temp button to max hot, wait a few seconds to let it fully open than go to max cold and repeat several times. This did the trick for my TL when I first bought it.