I just repaired a similar problem on my wife's '99 Solara. Her's was a Bank x (don't remember 1 or 2) Sensor 1. The Sensor 1's are before the catalytic converter, maybe even on the exhaust manifold(s). The Sensor 2's are after the catalytic converter(s).
1. The O2 sensors monitor and control the fuel/air ratio. They have internal heaters to get the sensors up to operating temperature quicker than the exhaust heat alone would. The engine computer monitors the heater circuit and detects a burnt-out heater. The O2 sensor may still be functional with exhaust heat.
2. Replace the sensor. If you want to, you may be able to confirm that the heater is bad and that you don't have a bad connection. On my wife's car, the Sensor 1 had a 4 wire connection - the 2 blue ones were the heater and the black and white were the sensing leads. Using a VOM across the blue wires, the old sensor measured open. The new sensor measured around 10 ohms.
3. Googling around, I found good info on www.toyotanation.com for the Solara. I found people recommending the Denso, not Bosch, so I bought it on-line. There is also a site www.rav4world.com that may help. (Also, after the fact, I found instructions for an easier way to replace it.) You may be able to rent/borrow the special sockets from an auto parts store if you DIY.