Archive for March 9th, 2007

Audi A3 1.8 lambda probe (oxygen sensor)

Posted in Audi, Audi A3, Audi Specialist, Follett on 03/09/2007 06:35 pm by FollettmotorsVWAudiBlog

Audi A3 1.8 (2002) Lambda probe (oxygen sensor)

Audi A3 1.8 Lambda sensor (oxygen sensor) close-up

Picture 1 (top) and Picture 2 (above)


Lamba probes (oxygen sensors) and the contaminated fuel debacle

Much has been written over the past few days about the fuel contamination debacle, with the latest twist of events coming in the form of full-page newspaper apologies and offers of compensation to those affected. It is believed that the fuel was contaminated with extraordinarily high levels of silicon.
Whilst newspaper reports cited comments from an official at the AA to say that they “had found that Ford and Volkswagen models did not appear to be affected by the fuel problem” it is still worth looking, nevertheless, at the particular part which appears to have been the ‘victim’ in all this.

Picture 1: this shows a lambda probe (also known as a ‘lambda sensor’ or ‘oxygen sensor’) from an Audi A3 1.8 (2002)
Picture 2: :a close-up of the lambda probe. Note the sampler vents at the end of the probe (indicated by arrow)

**Note - the lambda probe pictured above is NOT one of those affected.

What is a lambda probe? What function does it play?
The lambda probe (sensor 1) is an oxygen sensor that is screwed into the exhaust system between the engine and catalytic convertor. It is electrically connected to the car’s engine management computer - ECU (Electronic Control Unit).
The lambda probe generates a voltage when the exhaust gases pass over it. The voltage varies according to the oxygen content of the burnt exhaust gases. By this method, the ECU can detect whether a lean (:too little) or rich (:too much) fuel mixture is being introduced to the engine and can correct it to the ideal 14.7 parts air to 1 part fuel at operating temperature.

What is Lambda?
The ideal of 14.7 parts air to 1 part fuel is called ‘lambda’.

Why could a lambda probe have failed in this instance?
One of the main ways in which a lambda sensor can fail prematurely is if it comes into contact an excess of silicone or silicates - for example, silicone from internal coolant leaks or through using silicone sprays or gasket sealers on the engine or on the exhaust system close to the catalytic convertor.