To access the heater core in this model there is an extensive amount of work thats required to get to that point and this even requires removal of the front seats and pull back the carpet to remove the rear heater duct work. Below are directions:
Drain the coolant.
Remove 3 fasteners from the drivers side under dash insulator.
Rotate the lamp. Remove the lamp from the insulator.
Tighten Tighten all the screws to 1.5 N·m (13 lb in).
Tighten Tighten the screws to 1.5 N·m (13 lb in).