While I was gone, my wifes Camaro broke Down, she didnt tell me it was acting up, well I told her to take it to a mechanic I knew, He did a tune up and some other stuff, one of the things was clean the throttle body, well she was driving up to VA, I'm still gone, it throws a code, she takes it to a mechanic in NC, he say's the car told him it had a O2 Sensor Error, and the Catalitic converter is rattleing, well I come home, yes the cat is rattling but not a lot, but the code I'm getting is P0420, Catalist Below Threshold left bank, a code at a sensor before the Cat?!?! I've checked every thing I can think of, and nothing seems to be bad, can that cat, behind the sensor, cause the sensor tp throw this code??

Thanks Guys (This is why I hate computer comtrolled cars)

Otto