rasta420

There's a check engine light in my 98 Avalon, and its PO135. The description is: Heated O2 sensor heater circuit malfunction (bank 1,sensor 1). Autozone says that I need to replace both O2 sensors. Is this true? I think there is one O2 sensor on each exhaust manifold before the cat converter, so which one would I need to change? I'm really not trying to dish out the $140/each Toyota is asking for. Thanks