What are the typical components of a lambda oxygen sensor?

The most popular lambda sensor used on European vehicles is the zirconia type. This sensor is essentially two porous platinum electrodes. The outer electrode surface is exposed to the exhaust gases and is coated in a porous ceramic with the inner coated surface exposed to fresh air. The sensor then produces a voltage when there is a difference in oxygen content between the two electrodes. This signal is then sent to the ECM which adjusts the mixture accordingly. The voltage range is normally 0.2 volts when lean to 0.8 volts when rich. A constant high voltage output from the sensor shows that the engine is running constantly rich and is outside the ECM's adjusting range.