The Three-Way Catalyst (TWC) is used to help control exhaust emissions, i.e. you can clean the exhaust if you wish. The PCM (Powertrain Control Module) uses the signal from the number 2 oxygen sensor to monitor the effectiveness of the catalyst. If the Powertrain Control Module detects no difference in exhaust quality between the oxygen sensors, it indicates that the catalyst is not working properly.
It should be noted that this diagnostic code does not mean that the catalytic converter is defective because this tool cannot be broken frequently.
Basically, this code indicates the voltage of the signal produced by the oxygen sensor in bank two is below, which is considered normal for this sensor.
The O2 has four wires; one of them provides a 5-volt reference signal, one for the ground, one for the power circuit, and one ground circuit for the oxygen sensor heating element. When the oxygen content changes, the resistance in the sensor signal circuit also changes. This varying resistance affects the 5 volts in the reference signal circuit. The power train control module (PCM) monitors this signal. Thus, it determines whether the catalyst is operating correctly. If the PCM concludes that the signal voltage of the oxygen sensor two does not operate to the set degree, the fault code P0157 OBD2 is set.