O2 Sensor Heating
The oxygen sensor conductivity is efficient when it is heated 250° - 300° C (482 - 572°F). Because of this reason, the sensors contain heating elements. These "heated" sensors reduce warm up time, and retain the heat during low engine speed when the exhaust temperature is cooler. OBD II requires monitoring of the oxygen sensor heating function and heating elements for operation.
The two oxygen sensor heating circuits receive operating voltage from the Main Relay when KL15 is switched "ON". Each of the sensor heaters is controlled through separate final stage transistors.
The sensor heaters are controlled with a pulse width modulated ground during a cold engine startup. This allows the sensors to be brought gradually up to operating temperature. This helps reduce the possibility of thermal shock. The duty cycle is then varied to maintain the heating of the sensors.
When the engine is decelerating (closed throttle), the EMS2000 increases the duty cycle of the heating elements to compensate for the decreased exhaust temperature.