Ho2S Sensor 1
This vehicle uses wide-band lambda sensors to monitor oxygen content of the exhaust gas stream. These sensors compare the oxygen content of exhaust gas to the oxygen content of fresh reference air. The heated oxygen sensor has a fixed voltage on its signal wire, but varies the pump current to the oxygen sensor to indicate the vehicle's current air/fuel ration. The ECM interprets this current as a lambda value where a lambda of 1 means a stoichiometric ratio (14.7:1). A value higher than 1 indicates a lean condition, and a lambda less than 1 indicates a rich condition. During closed loop operation, the ECM compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. These oxygen sensors do not switch between rich and lean states to drive to a commanded air/fuel ratio. The use of the lambda gives a very precise air/fuel reading, and allows the vehicle to quickly reach the commanded state without switching.
When the engine temperature is below 37°C (99°F), the vehicle operates in open loop. The ECM begins pulsing the oxygen sensor heater ground to minimize the time it will take to reach closed loop fuel control. The oxygen sensor should begin functioning within 12 seconds after the heater reaches the proper temperature for operation. The heater is activated at key On.