Most likely bad Bank 2 upper O2 sensor. About $70.
Change this. Bank 2 (radiator side) upstream O2 sensor. You need a 22 mm or 7/8 inch or O2 sensor socket.
Bank 2 Upper O2 sensor;
On this 2-D picture, ignore the red box and arrow, the Bank 2 Upper is the sensor on the left of the pre-cat. The arrow is pointing to the Bank 2 pre-cat
Originally posted by chongo:
Edit. Per TSB, it could be any of these reasons but for a 10 year old car, it is very likely to be a bad O2 sensor.
The HEGO Sensor is monitored for switching. The code will set when the HO2S fails to switch due to circuit or fuel at or exceeding a calibrated limit.
Electrical:
�· Short to VPWR or VREF in harness or HO2S
�· HO2S circuit shorted to Ground
�· Water in harness connector
�· Open circuit
�· Corrosion or poor mating terminals and wiring
�· Damaged HO2S
�· Damaged PCM (other DTCs should be present)
Fuel System:
�· Excessive fuel pressure (stuck fuel pressure regulator, restricted fuel return lines, etc.)
�· Leaking/contaminated fuel injectors or fuel pressure regulator
�· Low fuel pressure or running out of fuel (fuel pump concern, fuel supply line restrictions, low fuel level, etc.)
�· Vapor recovery system (stuck VMV, etc.)
Induction System:
�· MAF contamination
�· Air leaks between MAF and throttle plate
�· PCV system / Other vacuum leaks
�· Improperly seated engine oil dipstick
EGR System:
�· Leaking gasket
�· Stuck EGR valve / Leaking diaphragm or EVR
Base Engine:
�· Oil overfill
�· Incorrect cylinder compression
�· Exhaust leaks before or near the HO2S
�· Secondary air stuck on 
