Method of controlling and diagnosing the heater of an engine exhaust gas composition sensor

A method of controlling and diagnosing a heater of a sensor sensitive to the composition of the exhaust gas of an engine;

• said method comprising the steps of:
• providing a sensor with a heater, the sensor comprising at least an electrolytic cell, which has two terminals and is sensitive to oxygen ions;
• measuring an air to fuel ratio (λ) of the mixture supplied to the engine by means of said sensor;
• calculating an internal resistance value (RPVS) of the cell on the basis of detected values of voltage at the terminals of the cell before supplying a reference current (IREF) to the cell and after a predetermined amount of time from the supplying of said reference current (IREF);
• calculating a corrected internal resistance value (RPVSc) of the cell according to the measured air to fuel ratio (λ);
• converting the corrected internal resistance value (RPVSc) into a current temperature value (TTIP) of the sensor;
• feedback controlling the temperature of the sensor by regulating the current supplied to the heater by processing any deviation (ΔT) between said current temperature value (TTIP) and an objective temperature (TOB);
• and
• diagnosing efficiency of the heater by comparing said current temperature value (TTIP) with at least one predetermined value (TSOGLMIN, TSOGLMAX).