Check Engine Code

[Raptor 22]

P0135 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) read by Auto Zone. How reliable? Where is sensor located. Sorry, I have not had a chance to work on the wife's '94 ES-300 yet and now the code has set. Checked gas cap - tight. Have a factory manual set and Scan Tool for my laptop on the way (hurry mr UPS)

[SKperformance]

that should be the o2 sensor at the rear of the engine

by the firewall

as per jpi

that is the first bank