Rick's Free Auto Repair Advice

Clean an oxygen sensor

Can you clean an oxygen sensor?

Technically yes. But in reality no. The pores in the gas permeable electrodes allow oxygen ions to pass through, but they are so small that no cleaning solvent can possibly penetrate and clean them. In other words, if the pores are clogged, they stay clogged. Do a search for cleaning an oxygen sensor and you’ll see all kinds of advice on how to clean oxygen sensors. They’re all worthless.

Those posts show you how to clean the external shield. Great, that gets you zip as far as increased performance. The shield is there to protect the ceramic structure from physical damage.

The posts also show using a spray cleaner to clean the internal oxygen sensor components. These cleaning methods display a complete lack of understanding on how oxygen sensors and air fuel ratio sensors work. The liquid cleaner may possible flush off a surface coating of carbon from the ceramic structure and external platinum electrode, but trust me; if the coating is that bad that you think it should be cleaned, the pores in the electrode are already permanently clogged. The only way to restore performance is to fix the underlying cause of the excessive carbon and then to replace the oxygen sensor or air fuel ratio sensor.

Understand how an oxygen sensor is built

Oxygen sensors are constructed with a ceramic cylinder that’s plated on the inside and outside with porous gas permeable platinum electrode and protected by an exterior shield with either holes or slots. One electrode is exposed to exhaust gas, while the other is exposed to outside air. The difference in oxygen concentration causes electrons to flow through the ceramic element. The temperature of the ceramic affects its ability to inhibit or conduct the electron flow.

A voltage is produced by the difference in the two amounts. If the amount of oxygen in the exhaust is closer to the amount in the air, the engine is lean and the voltage is low (normally 0.1 to 0.3 volts). If the engine is rich the voltage is high (generally 0.8 to 0.9 volts).

Oxygen sensors fall into two groups; narrow band and wide band. The narrow band sensors, as the name implies detect a very narrow band of oxygen levels, so the computer gets either a “high” or “low” oxygen level reading from the exhaust. Upstream barrow band sensors are used in older vehicles and have been replaced by wide band air fuel ratio sensors. However, some car makers still used narrow band sensors on the downside, after the catalytic converter.

Three types of narrow band oxygen sensors

All narrow band oxygen sensors (also referred to as Nernst cell) compare the amount of oxygen in the exhaust to the amount of oxygen in the outside air. So every narrow band oxygen sensor has either a port to the outside or a gap in the wire insulation to allow outside air into the sensor for the comparison.

Zirconia dioxide oxygen sensor

Zirconia oxygen sensors generate a voltage that varies in direct proportion to the oxygen concentration in the exhaust. When oxygen concentration is low, the sensor produces a low voltage. When oxygen concentration is high, it produces up to 1-volt. Zirconia conducts the flow of oxygen ions when the material is above 350°C. The outside of the zirconia cell is exposed to the exhaust gas while the inside is exposed to outside air. Once at operating temperature, oxygen ions pass through the ceramic structure to the internal platinum electrode and deposit their charge, thus generating a voltage that’s read by the PCM.

Planar oxygen sensor

A planar sensor is a zirconia sensor with a heater to speed up its ability reach operating temperature. A planar sensor can become active within 12-seconds after the engine is started.
Titania. A titania sensor operates differently than a zirconia sensor. Rather than generating 0-1-volts as oxygen concentration varies, the titania sensor changes the input voltage supplied by the PCM through the use of a variable resistor. A variable resistor changes its resistance based on the concentration of oxygen in the exhaust stream. So the PCM supplies 5-volts to the Titania sensor, the variable resistor decreases resistance as it encounters a lean exhaust (more oxygen), which returns a high voltage signal to the PCM. As oxygen levels fall, the sensor increases resistance so the PCM sees a lower return voltage signal. The PCM sees voltage near 5-volts as a lean condition and voltages near 0 as a rich condition.

Wide Band Air fuel ratio sensor

Like a narrow band sensor, wide band air fuel ratio sensors also compare the compare the amount of oxygen in the exhaust to the amount of oxygen in the outside air. But unlike narrow band sensors, wide band sensors don’t rely on natural air movement to provide the comparison. They use an electrochemical gas pump to move outside air through the sensor so it can provide a much more accurate comparison. The electrochemical pump has a feedback circuit to control pump current which helps the PCM determine oxygen content of the exhaust. So it’s really a much more sophisticated combination of Zirconia and Planar sensor.
Rather than monitor voltage changes, an air fuel ratio sensor monitors CURRENT flow, which is directly proportional to the oxygen concentrations in the exhaust stream. The current flow varies from 0-30mA.

None of these oxygen sensors or air fuel ratio sensors can be cleaned in a way that will affect performance. You can clean it to make the exterior shield look shiny. You can spray cleaner on the ceramic element. That may make you feel good. But it will do NOTHING to improve performance. It’s a complete waste of time and energy.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat

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