One problem related to defogger controls has been reported for the 2004 Toyota Highlander. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Toyota Highlander based on all problems reported for the 2004 Highlander.
The temperature control on my 2004 Toyota Highlander keeps switching by itself from hot to cold and hot again. I have to actually turn the ac on even when the outside air coming in is moderate because the temperature control will switch by itself to hot and I can't switch it off. This occurs every time I drive and more so when I go over a bump or make a turn. I turn the vent on for outside air, but the temperature control gets locked on to hot and I can't turn it off. I have called the dealer and they have said that it would cost around $1000. 00 to fix it. They want to replace the whole control unit. I have read various forums of numerous owners having this same issue. It seems to be a problem with Toyota not leaving enough slack in a ribbon cable with 3 connections that connect from the circuit board to the control knob. The wires break off from the soldering on the knob. This sounds like a known defect to me that Toyota is aware of, but chooses to ignore. Apparently a cheaper fix is to re-solder the cable, but they refused to do that. I think they should be fixing this for free. This is just another example of Toyota ignoring known issues with their vehicles.