How to Test Whether an Oxygen Sensor is Good or Bad?

[MacAdam]

To test whether an oxygen sensor is good or bad, unplug the oxygen sensor connector and observe whether the engine fault disappears. Below is a detailed introduction to the oxygen sensor: Overview of the Oxygen Sensor: The automotive oxygen sensor is a critical sensing component in the electronic fuel injection engine control system. It is a key part in controlling vehicle exhaust emissions, reducing environmental pollution caused by vehicles, and improving the fuel combustion quality of the car engine. Oxygen sensors are installed on the engine exhaust pipe. Main Functions of the Oxygen Sensor: The oxygen sensor enables the engine to obtain the optimal concentration of the air-fuel mixture, thereby reducing the emission of harmful gases and saving fuel. By measuring whether there is an excess of oxygen in the exhaust after engine combustion, the oxygen sensor converts the oxygen content into a voltage signal and transmits it to the engine computer, allowing the engine to achieve closed-loop control targeted at the excess air factor.

[FinleyAnn]

Last time I checked the oxygen sensor, I used a multimeter to measure the voltage. When starting a cold engine, the voltage should stabilize around 0.45V, and after warming up, it should start fluctuating between 0.1-0.9V to be considered normal. If the voltage doesn't change or stays at 0.5V, it's likely that the sensor is faulty. Remember, the front oxygen sensor measures data fluctuations at the front of the exhaust pipe, while the rear oxygen sensor checks catalytic converter efficiency at the rear—don't mix up their positions. Using a diagnostic tool to view the data stream is more intuitive; at 2000 RPM, the front oxygen sensor's voltage fluctuation frequency should change more than 8 times within 10 seconds. Aging rubber sleeves can cause it to misread oxygen concentration, so this also needs attention, as it affects fuel consumption and emissions.

[AlexandraAnn]

It's actually not difficult for us car owners to perform the inspection ourselves. Start the engine and wait for the coolant temperature to rise, then unplug the sensor connector to examine these four pins. Use a multimeter to measure the heating resistance - typically 2-14 ohms is normal, and no resistance in the heating circuit indicates a burnout. After reinstalling it, connect a diagnostic tool to read the trouble codes - codes P0130 through P0167 all indicate oxygen sensor issues. Exhaust leaks can also cause false readings, so it's worth checking the exhaust pipe connections. For older vehicles, oxidation at the connections often leads to poor contact - removing them and spraying with precision electrical cleaner can often restore functionality.

[AsherDella]

Oxygen sensor testing focuses on signal response speed. At hot idle, the voltage should fluctuate between 0.1V-0.9V, changing at least 6 times within 20 seconds. Using an oscilloscope provides the most accurate waveform reading - a healthy upstream O2 sensor's waveform resembles dense square waves. Infrared thermometer measurements of exhaust pipe temperature can assist diagnosis - if the sensor doesn't function when the catalytic converter front section reaches 380-650°C, it's faulty. Always apply anti-seize compound during replacement. Last time my apprentice forgot the lubricant and the threads seized solid.