Lambda sensors were first fitted to cars in 1977 to improve the efficiency of combustion engines and help to reduce harmful exhaust emissions such as carbon monoxide.
Lambda sensors operate by measuring the amount of oxygen in the exhaust. An efficient engine requires a specific amount of air and fuel in it’s cylinders at combustion. The perfect ratio being 14.7:1 (14.7 parts air to 1 part fuel). This perfect mixture is called Lambda and this is where the unusual name originates. However, they are often also called oxygen sensors or O2 sensors due to their fundamental role of measuring oxygen. The levels calculated by the Lambda are sent as data to the ECU which then calculates and determines how best to achieve the ideal mixture of air and fuel at combustion.
An incorrect air/fuel mixture will be either rich or lean:
• In a rich mixture the air is high in unburned fuel, though low in oxygen.
• A lean mixture has the opposite balance and is high in oxygen due to not enough fuel being injected.
Many vehicles now feature a pre-cat Lambda Sensor and a post-cat Lambda Sensor. Whilst the pre-cat Lambda Sensor communicates to the ECU regulating the air/fuel ratio; the post-cat Lambda Sensor performs a diagnostic role, monitoring the Catalytic Converter.