O2 sensor (lambda sensor) for your car

Small component, huge effect

The lambda sensor, alternatively called oxygen sensor, may not be a very big component, but it carries a lot of responsibility for engine performance and efficiency; as only with the correct measuring values the mix of fuel and air is correctly composed. Ignoring malfunctions not only does make you an environmental criminal, because the exhaust values no longer are within the acceptable norm; furthermore, it is economically detrimental as the engine needs considerably more fuel.

Facts about the lambda sensor in an overview:

Where is the oxygen sensor situated?

• The lambda sensor or oxygen sensor sits in a bracket at the bottom of the car directly in front of the catalytic converter. A sensor can be placed behind the converter as well. This would be a diagnostic sensor. In some cars it has some kind of housing, but generally it lies free and can be easily spotted.

How does it function?

• The sensor sits directly in the exhaust flow which is guided through a zirconium membrane and a Nernst cell (named after Walther Nernst). The amount of oxygen molecules is compared to the actual environmental air to determine the proportion of combustion air. This value is called "lambda value" in professional terms.

What happens in case of a defect?

• First, the fuel consumption rises and the engine performance deteriorates.
• Initially possibly imperceptibly, gradually stronger and stronger.
• The engine regularly stutters or stalls.
• If the proportion is no longer accurate, the engine check light goes on.
• In extreme cases the engine stalls or can only be started with difficulty.

Possible causes

• Most oxygen sensors sooner or later suffer from general material ageing. Particles clog the membrane and the Nernst cell, and the measuring performance falls.
• Mechanical stress can destroy the lambda sensor as well if the car bounces too deep.
• Electric damage through short circuit of a defective cable can completely disable the sensor.

To the garage or DIY replacement?

• In older cars until halfway the first decade of 2000 DIY replacement is possible, provided a ramp or hoist is available.
• In modern cars you need a special ring-shaped connection or the cable must be cut and re-connected at assembly.
• Upon installation a visit to the garage is required to have the fault memory deleted and the software initialised.

Still driving with a defective lambda sensor

If you still manage to ignore the symptoms (which is difficult) and continue driving with a defective lambda sensor, you might be in for a nasty surprise at a possible traffic control or MOT inspection, as a car is only fit for traffic if exhaust values are within the acceptable levels. If deliberate negligence can be proven, fines for tax evasion are possible.

Differences between spare parts

Two different versions are currently available on the market and used by car manufacturers:

• The conventional (zirconia) lambda sensor uses the electric voltage change to measure the remaining oxygen. The probe needs an operating temperature of approximately 350ᵒC. Its measuring spectrum is rather small and not suitable for all engines.
• The wideband sensor is the modern version of the lambda sensor. Its measuring spectrum is wider and the sensor is suitable for petrol, diesel and even gas engines. Modern cars often have several of these wideband sensors (differential measurement) installed.

Both probes can be either a finger-shaped or a planar probe. The former is a bit sturdier as its housing often has a protective tube, protecting the sensor against combustion residue and condensing moist. The latter heats up more quickly, but is less sturdy on the other hand.

What costs can you expect?

As a driver you hardly have any influence on the life span of the lambda sensor and you have to fall back on the manufacturer's specifications. For cheap products they lie at approximately 160.000 driven kilometres, for high-quality spare parts - at c. 250.000 kilometres. The price spectrum is equally wide, starting at 50 EUR (c. £45) reaching up to 100 EUR (c. £90). Choosing for a premium product allows you to considerably reduce exhaust values and fuel consumption. If you consider the price too high, we invite you to have a look in our shop. Here you find all kinds of lambda sensors for all cars at prices which lie lower than the recommendations of manufacturers.