As part of the vehicle's closed loop (or feedback control) system, the oxygen sensor monitors the density of oxygen in the exhaust gas. The sensor consists of a closed-end tube made of ceramic zirconia and other components. Porous platinum electrodes cover the tube's inner and outer surfaces. The tube's outer surface is exposed to the exhaust gases in the exhaust manifold (or, if so equipped, just beyond the turbocharger). After detecting the amount of oxygen in the exhaust gas, the oxygen sensor outputs an electrical signal to the engine control unit.