If the front oxygen sensor shows a low voltage of around 0.2 volts and the rear sensor shows a high voltage of 0.8 volts, what could this indicate?

The observation of a low voltage reading from the front oxygen sensor at approximately 0.2 volts, combined with a higher voltage reading of 0.8 volts from the rear oxygen sensor, suggests that the catalytic converter is likely inefficient or may be failing.

In normal function, the front oxygen sensor monitors the air-fuel mixture entering the engine, while the rear oxygen sensor monitors the exhaust coming out of the catalytic converter. A low voltage reading from the front sensor often indicates a rich fuel mixture at the engine side, where there is too much fuel compared to air. This is contrasted by the higher reading from the rear sensor, which could indicate that the catalytic converter is not performing properly in converting the richer exhaust gases into less harmful emissions.

When the catalytic converter operates efficiently, the readings from the front and rear sensors should differ as the converter cleans the exhaust gases. If the front sensor shows a continued low voltage and the rear sensor shows a high voltage, it indicates that the conversion process is not occurring effectively, pointing towards potential catalytic converter failure or inefficiency.

This scenario highlights the critical role of the catalytic converter in reducing emissions, and the readings from the oxygen sensors serve as key indicators of its operational status.