Where is the Air-Fuel Sensor Heater Circuit on a tacoma?

It's located on the exhaust pipe, just after it comes out of the engine, and just before the catalytic converter. The sensor itself it bolted into the exhaust pipe and it has a connector with a few wires coming out of it. You can access it from the engine compartment on the drivers side, but you may want to approach it from underneath to remove it. Hope that helps.