Bosch Motronic - Component Datasheet

Oxygen / Lambda Sensor (G39)

The oxygen sensor (also commonly referred to as the O2S) resides in the exhaust pipe near the output of the turbocharger. It measures the amount of un-burnt oxygen in the exhaust gas in order to regulate the fuel-air mixture for optimum performance & economy compromises.

The theoretical value for optimal fuel-air mixture is 14.7 parts air to one part fuel. This ideal or target value can also be described as a 'lambda' value of 1.0. Higher lambda values reflect a more lean mixture whilst for situations when the engine can be more fuel efficient. Lower lambda values reflect a more fuel rich mixture which is adopted by the ECU in high load situations to ensure good engine performance and avoidance of knock.

The ECU continually monitors G39 to determine the operating lambda value. The engine's ignition, injection and boost maps are dynamically adapted by the ECU with knowledge of the lambda value so that the eternal compromise between fuel economy and performance is safely and cleverly sought after.

Should the oxygen sensor, or its associated heater element (Z19), fail then the ECU simply uses the most recent lambda value before the time of failure for ongoing calculations.

Follow this link for lambda probe info on SJM's site.