What is indicated by a significant increase in voltage from an oxygen sensor during operation?

A significant increase in voltage from an oxygen sensor during operation indicates a rich air-fuel mixture. Oxygen sensors play a critical role in monitoring the level of oxygen in the exhaust gases, which allows the engine control module (ECM) to adjust the fuel mixture for optimal combustion efficiency.

When the air-fuel mixture is rich, meaning there is more fuel compared to air, the oxygen sensor generates a higher voltage signal, often above 0.5 volts. This higher voltage indicates that there is less oxygen present in the exhaust gas because the fuel has not been completely burned, prompting the ECM to reduce the amount of fuel injected into the engine to correct the mixture.

In contrast, a lean air-fuel mixture would produce a lower voltage output from the sensor, suggesting there is more oxygen present in the exhaust because the mixture is less fuel-rich. Normal operation would typically be indicated by a steady voltage that oscillates around a predetermined range, reflecting a balanced air-fuel mixture. A sensor malfunction might show erratic voltage patterns, consistent readings at high or low values without fluctuation, or failure to respond to changes in the exhaust conditions.