Direct O2 Sensor Heating

The ECM uses internal final stage control for oxygen sensor heating. OBD II requires that the oxygen sensor heating function be monitored for operation.

The four oxygen sensor heating circuits receive operating power from the ECM relay when KL 15 is switched ON. Each of the sensor heaters are controlled through separate final stages. The sensor heaters are controlled with a pulsed square voltage during a cold start. This allows the sensors to be brought up to operating temperature without the possibility of thermal shock. The duty cycle is then varied to maintain the heating of the sensors.

When the engine is in deceleration (closed throttle signal present), the ECM determines the exhaust temperature is lower than when the hot exhaust gas is flowing through the exhaust system.







The control module increases the duty cycle of the heating elements to compensate for the decreased exhaust temp. The increase in duty cycle is based on a programmed map.