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The Chevy Silverado trouble code P1133 points to an issue with the Heated Oxygen Sensor (HO2S) on bank 1, sensor 1. When this sensor doesn't switch properly, it can affect the fuel mixture being sent to the engine. A malfunctioning sensor can lead to reduced fuel efficiency, unpleasant exhaust odor, engine performance issues, and could cause your vehicle to fail emissions tests. The oxygen sensor in question is situated on the right-hand side of the engine by the firewall, placed in the exhaust system between the engine and the catalytic converter. To replace the sensor, you'll need a 22-millimeter deep well socket and ratchet. Start by disconnecting the electrical connector, then use the socket to unscrew the sensor in a counterclockwise direction. When installing the new sensor, ensure it is hand tight to avoid cross-threading, then use the socket to tighten it an additional half to 3/4 turn.
In some cases, the code P1133 for OBD II is specific to certain manufacturers. This code usually indicates a problem with the heated oxygen sensor and is triggered when the powertrain control module notices a lack of switching between rich and lean fuel cycles.