P042A - Catalyst Temperature Sensor Circuit Bank 1 Sensor 2

P042A is set when the Engine Control Unit (ECU) detects an implausible signal from the Exhaust Gas Temperature (EGT) sensor located after the catalytic converter (Sensor 2) on Bank 1. The sensor is a thermistor that changes resistance relative to temperature. The ECU supplies a reference voltage (typically 5V) and monitors the return signal. If the signal voltage remains outside the calibrated range (e.g., below 0.2V or above 4.8V) for a specific duration, the code is stored. This sensor is critical for monitoring catalyst efficiency and managing DPF regeneration cycles.