1992 and has been widely used for car engine management systems in order to meet the ever-increasing demands for better fuel economy, lower emissions and better engine performance at the same time. It is based on a planar zirconia element, but also incorporates an electrochemical gas pump. An electronic circuit containing a feedback loop controls the gas-pump current to keep the output of the electrochemical cell constant, so that the pump current directly indicates the oxygen content of the exhaust gas. This sensor eliminates the lean–rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry this sensor is also called a UEGO (universal exhaust-gas oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air–fuel display equipment. The wideband zirconia sensor is used in stratified fuel injection systems and can now also be used in diesel engines to satisfy the upcoming EURO and ULEV emission limits. Wideband sensors have three elements: ion oxygen pump, narrowband zirconia sensor, heating element. The wiring diagram for the wideband sensor typically has six wires: resistive heating element, resistive heating element, sensor, pump, calibration resistor, common. Titania sensor A less common type of narrow-band lambda sensor has a ceramic element made of titania (titanium dioxide). This type does not generate its own voltage, but changes its electrical resistance in response to the oxygen concentration. The resistance of the titania is a function of the oxygen partial pressure and the temperature. Therefore, some sensors are used with a gas-temperature sensor to compensate for the resistance change due to temperature. The resistance value at any temperature is about 1/1000 the change in oxygen concentration. Luckily, at λ = 1, there is a large change of oxygen, so the resistance change is typically 1000 times between rich and lean, depending on the temperature. As titania is an N-type semiconductor with a structure TiO2−x, the x defects in the crystal lattice conduct the charge. So, for fuel-rich exhaust (lower oxygen concentration) the resistance is low, and for fuel-lean exhaust (higher oxygen concentration) the resistance is high. The control unit feeds the sensor with a small electric current and measures the resulting voltage drop across the sensor, which varies from nearly 0 volts to about 5 volts. Like the zirconia sensor, this type is nonlinear, such that