Should be easy to sell a one-owner, low mileage '02 Highlander in very good shape and good running condition, except....?
Keep driving it. It barely costs you anything to insure. You can still drive it as is but it might be a good idea to go to a different mechanic have the lights checked and it can be something as simple as a dirty sensor. If it is something different and is too expensive to fix then just live with it as long as the car gets you from point a to b.
That's total BS that a factory trained mechanic can't fix the problem. You don't even list the codes stored in the computer jojo.
If the price is right, it will be easy to sell.
Sell it "as-is" for $1500. Sell it if someone makes an offer close to that price. INFORM the buyer of the problems.
If the car was in good running condition, it would be easy to sell. But your car is not in good running condition, yours has both the check engine and vsc lights on. If you are in a state that requires an inspection or smog check, it's unlikely that you can sell the car at all. If you aren't in one of those states, you can sell the car. - the car in rough condition is valued about $2K. You should be able to get $1000-$1400 for it.