The Toyota Highlander uses two heaters whose cores may need replacing. The rear heater is slightly easier to get to, located near and below the rear console, but still requires removal of some components. The front heater is much more challenging, requiring removal of the whole instrument panel.
Tools Used: Tools, Replacement heater core, Wrench, Screwdriver, Engine coolant
Replace Heater Core
Rear Heater Core
Disconnect the Highlander’s negative battery cable. Drain the engine coolant into a clean container if you want to reuse it. Disconnect the heater hoses from the rear heater core.