[wizzer]

Sorry. No ideas about the engine light being related to the heater.

If I recall correctly, I was told by the dealer that the amber check engine light is frequently related to the Oxygen / O2 sensor. The Highlander has two and one of them is more likely to fail than the other.

If I recall correctly it costs a couple of hundred dollars to replace both and I don't know if it really does much good. If I recall correctly it just adjusts the fuel / air ratio during warm up so you might use a bit more fuel.