Technical Documents

Oxygen Sensors Explained

Oxygen sensors cannot be cleaned, that is why checking for and replacing a worn out or damaged sensor should be and important poart of every routine service.

Replacing a worn-out sensor will not only imporve a vehicle’s performance and reduce harmful exhaust emissions, but it can save hundreds of dollars a year in fuel costs.

We know that an oxygen sensor detects the amount of oxygen in the exhaust gas and sends a signal to the engine computer (ECM or ECU), which adjusts the air’fuel mixture to the optimal level.

Too much oxygen in the exhaust gases indicates a lean mixture, which can cause performance problems, including misfires. Too little oxygen indicates a rich mixture, which wastes fuel and results in excess emissions. Either condition can shortned the life of the expensive cataltic converter.

Almost all petrol powered vehicles between 1986 and 1996 have at least one oxygen sensor while newer vehicles often have two or four.

Not only are propertly functioning oxygen sensors good for the environment, but it’s confirmed that they can save money in fuel costs, provided they are serviced correctly.

An oxygen sensor is a wearing part with a specific service life, not unlike a spark plug. However they are often incorrectly viewed as a repair item. The will eventually die of “old age” but without regular checking and replacement their performance will greatly deteriorate.

A sensor should have a service life ranging from 50,000km to 160,000km dependant on design. Single and two wire sensors should be checked and/or replaced at 50,000km, three or four wire heated sensors at 80,000km, and wide band sensors at 160,000km. There are various conditions however that can dramatically reduce these life spans.

Exposure to carbon, dirt, dust, harmful gases, anti-freeze, chemicals, incorrect fuel, water and impact damage will shorten the life.

A common practice amongst some engine re-builders and panel beaters is to paint the oxygen sensor and its surround, which also causes contamination and “kills” the sensor. Any contamination of the oxygen sensor results in the coating of the platinum electrodes, which insulates them and slows the sensor response time down.

This causes the sensor to give a lower that average reading to the fuel/air mixture, giving the impression that the engine is lean, causing the fuel management system to overcompensate and drift the fuel ratio to rich.

The end result of old, worn, damaged or contaminated oxygen sensors is inevitably the same: higher fuel consumption, poor engine performance and excessive exhaust emissions.

The automotive oxyen sensor was invented by Bosch, which has manufactured over 400 million of them since 1976. The company points out that it is the world’s largest producer of oxygen sensors, supplying to virtually all vehicle manufacturers around the world, all manufactured to meet or exceed OEM specifications.

They utilise a mix of oxides including zirconium and yttrium to form a tough base that will withstand intense stress. Bosch advises that it has a huge range of direct-fit oxygen sensors plus a range of universal-fit oxygen sensors which cover more than 90% of the Australian market.

Bosch Oxygen Sensors

More information can be found in this Technical Guide orĀ on the Bosch website:

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