* Upstream (Pre-Catalyst) Sensors: These are located in the exhaust manifold or very close to it, *before* the catalytic converter. There's one for each bank.
* Downstream (Post-Catalyst) Sensors: These are located in the exhaust pipe, *after* the catalytic converter. There's one for each bank. Their primary function is to monitor the catalytic converter's efficiency, not to control the air/fuel mixture.
To find them:
The best way to locate them is to consult a repair manual specific to your Silverado's engine. A Haynes or Chilton manual will have diagrams showing the exact location of the sensors. You can also find diagrams online (be cautious of the accuracy of these, double-check with a reputable source).
Look for wire harnesses going into the exhaust system near the manifolds and after the catalytic converters. The sensors themselves are usually cylindrical and threaded into the exhaust.
Caution: The exhaust system gets extremely hot. Allow the engine to cool completely before attempting to locate or work on the oxygen sensors.
