Best place for OBDII code definitions?

Where's the best place for OBDII code definitions? I put in two brand new Ac/Delco pre-cat O2 sensors and now I am getting a P0134 code. One of them may be bad, but which one?

Do O2 sensors take a while to settle in, or should they be working right away?

Thanks

P0134 - O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
Bank 1 means the drivers side of the engine, sensor 1 means pre-cat. www.troublecodes.net They should be working right away. Check for a fully seated connector, or a bent pin. I might try having the code erased and see if it returns, if they are both brand new sensors. The computer may have to re-learn those new sensors.

Thanks. I had erased the code a few days ago, so I will be curious to see if it returns. If it does, I will take it out and look for a bent pin, as you suggest.

Thanks again.