Introduction to On Board Diagnostics (II)

Sensors and ActuatorsEmployed in OBD IIDiagnosticsExhaust Gas Oxygen (EGO) sensorThere are two types of EGO sensors, both based on the use of oxides of materials.One uses Zirconia (ZrO 2 ), and the other uses titanium oxide (TiO 2 ). But ZrO 2is most popular and is described here. The sensor consists of ZrO 2 sandwichedbetween two platinum electrodes. One electrode is exposed to exhaust gasin the exhaust manifold, and the other electrode is exposed to normal nair forreference. The electrode that is exposed to exhaust gas is coated d with porous protectiveovercoat.The ZrO 2 attracts oxygen ions and they accumulate on theZrO 2 surface just inside platinum electrode. AS oxygen ions are negativelycharged, there will be a potential across the two electrodes if the oxygen ionson exhaust gas side are less than the oxygen ions on the normal air side. Thepolarity of this voltage is positive on the exhaust gas side and negative on air side.The voltage depends on the concentration of the oxygen in the exhaust gas and theEGO sensor temperature.