Circuit Description

The Oxygen Sensor (O2S) is a sensor designed to create a voltage relative to oxygen content in engine exhaust stream. PCM supplies O2S 1 with signal and return circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When O2S detects that engine is operating rich, signal voltage is high and decreases the signal voltage as engine runs leaner. This oscillation at greater than and less than the bias voltage, sometimes referred to as activity or switching, can be monitored with O2S signal voltage.

The O2S needs to be at a high temperature in order to produce a voltage. Once O2S has reached operating temperature, the control module monitors the O2S bias, or reference, voltage as well as O2S signal voltage for closed loop fuel control. During normal closed loop fuel control operation, PCM will add fuel or lean out the mixture, when O2S detects a rich exhaust condition.

This DTC determines if O2S is functioning properly by checking for an adequate number of O2S voltage transitions greater than and less than the bias range of 300-600 millivolts within a given time frame. This DTC sets when PCM fails to detect a minimum number of voltage transitions at greater than and less than the bias range during the test period time frame.