With so many vehicles in use on our roads the reduction of pollutants produced by the internal combustion engine is of ever increasing importance. To encourage advances in technology that can bring this about governments have introduced progressively tougher exhaust gas emission legislation. Lambda sensors are a very important part of the technology used to achieve these legislated targets and as a result of their function the engine can also deliver the best economy and performance available. From the end of 1992 most petrol engine vehicles sold in the UK had Lambda sensors fitted.