What does code po157 mean on 5.7 Chevy engine?

The code P0157 on a 5.7 Chevy engine indicates a problem with the O2 (oxygen) sensor circuit, specifically the downstream sensor on Bank 2. This code suggests that the sensor is reporting a low voltage signal, which may indicate a fault in the sensor itself, a wiring issue, or a problem with the exhaust system. Addressing this code typically involves inspecting the sensor and its connections, and potentially replacing the sensor if necessary.