Two problems related to defogger controls have been reported for the 2003 Toyota Highlander. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Toyota Highlander based on all problems reported for the 2003 Highlander.
Temperature knob is loose causing heat to only work intermittently.
Heater control unit malfunction. Heat to cold switch stops working, dealer states that the whole heater control unit has to be replace. After extensive searching, I have found that the problem is when a nut becomes lose holding the control knob, it shakes and the wires break of make the unit stop working.