Ron- the B1S1 is on the rear exhaust manifold. You have to get to it from underneath, meaning, unless you have a lift, you'll have to jack the car up. You will readily see it facing to the passengers side up high where it's not easy to get to. You're east coast so you may have a problem with rust. I would definitely use whatever rust buster you feel is most effective and the longest box wrench you can get your hands on. The hardest part is getting the plug unplugged, it takes 2 hands and you can only get 1 up there. I would suggest getting help- one person on top to hold the wiring loom taunt and the other on the bottom to pull on the plug. Otherwise you'll go nuts trying to do it alone. You may need to try to wedge something small in the locking tab on the plug so you are able to pull with 1 hand while someone holds from the top with 1 hand (neither of you can get 2 hands in there) I also suggest getting the sensor online where you can buy it for around $150. That's for original eq. Denso, the only thing I would recommend. I just noticed you have an ES rather than RX. Don't know how much different that will be, have to jack it up and see. That code is only the heater, so it's not urgent, won't hurt anything, may only run faintly rougher when cold.