OXYGEN SENSOR OUT OF SPECIFICATION HEATER RATIONALITY MONITOR USING COLD START CYCLE

Vehicle oxygen sensor heater diagnostic techniques comprise, upon detection of a set of cold start conditions of the vehicle, measuring an initial resistance of each of a set of two or more oxygen sensor heaters and determining whether any of the measured initial resistances is outside of a nominal resistance range. In response to an outlier oxygen sensor heater being outside of the nominal resistance range, each of the set oxygen sensor heaters is provided with an equal voltage for a period, the resistance of each of the set of oxygen sensor heaters is monitored during the period, and a malfunction of the outlier oxygen sensor heater is detected or matured when a difference between its resistance and the resistances of the other oxygen sensor heaters after the period is greater than a calibrated threshold.