This vehicle has a thermostat that fails in the open position which causes the temp gauge to drop below normal and heater to fail. The thermostat is located on the driver's side of the engine behind the alternator. You might need to remove the wheel to access the mounting bolts. You will need multiple rachet extensions and some patience. Dealer wants $500 to replace thermostat. Do it yourself for less than $100.
service engine light came on. was told it could need engine coolant or was the thermostat. let problem go with out doing anything. bout a year later had to have a catalytic converter replaced. do not ignore engine lights. cost way more down the road