Which O2 sensor
 

The 04 Impala is throwing a code for a bad O2 sensor, but we're not sure which one. This vehicle has 4 of them.

Is there a DIY method of determining which one is having problems?

Thanks for the help.

Use a scangauge to get the engine code or go to the local autoparts store and have them read the code for you. That will tell you which one is bad.

Check the codes and get them defined. If the definition is sensor 1 Bank 1 it's the upstream sensor for cylinders 1-3, if the definition is sensor 1 bank 2 it's the upstream sensor for cylinder 4-6, if it's sensor 2 bank 1 it's the downstream sensor for cylinders 1-3, and if it sensor 2 bank 2 it's the downstream sensor for cylinders 4-6. The upstream sensor is the pre catalytic converter sensor and the downstream sensor is the post catalytic converter sensor.

Ah, so the code should tell us which is the bad one. We had the code read somewhere, and were told that the faulty sensor could not be specified by the code alone. Thanks for clarifying.