exception of some turbocharged models), inputs from the air flow meter are also ignored, as they might otherwise lower engine performance due to the mixture being too rich or too lean, and increase the risk of engine damage due to detonation if the mixture is too lean. Function of a lambda probe Lambda probes provide feedback to an ECU. Where applicable, gasoline, propane and natural gas engines are fitted with three-way catalysts to comply with on road vehicle emissions legislation. Using the lambda sensor signal, the ECU can operate the engine slightly rich of lambda = 1, this is the ideal operating mixture for a three way catalyst to be effective. Robert Bosch GmbH introduced the first automotive lambda probe in 1976, and it was first used by Volvo and Saab in that year. The sensors were introduced in the US from about 1979 and were required on all models of cars in many countries in Europe in 1993. By measuring the proportion of oxygen in the remaining exhaust gas, and by knowing the volume and temperature of the air entering the cylinders amongst other things, an ECU can use look-up tables to determine the amount of fuel required to burn at the stoichiometric ratio (14.7:1 air:fuel by mass for gasoline) to ensure complete combustion. The probe The sensor element is a ceramic cylinder plated inside and outside with porous platinum electrodes; the whole assembly is protected by a metal gauze. It operates by measuring the difference in oxygen between the exhaust gas and the external air and generates a voltage or changes its resistance depending on the difference between the two. The sensors only begin to work effectively when heated to approximately 316 °C (600 °F), so most newer lambda probes have heating elements encased in the ceramic that bring the ceramic tip up to temperature quickly. Older probes, without heating elements, would eventually be heated by the exhaust, but there is a time lag between when the engine is started and when the components in the exhaust system come to a thermal equilibrium. The length of time required for the exhaust gases to bring the probe to temperature depends on the temperature of the ambient air and the geometry of the exhaust system. Without a heater, the process may take several minutes. There are pollution problems that are attributed to this slow start-up process, including a similar problem