Circuit Description

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

The O2S 1 needs to be at a high temperature in order to produce a voltage. Once the O2S 1 has reached operating temperature, the controls module monitors the O2S 1 bias, or reference, voltage as well as the O2S 1 signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the controls module will add fuel, enriches the mixture, when the O2S 1 detects a lean exhaust content and subtract fuel, leans out the mixture, when the O2S 1 detects a rich exhaust condition.

This DTC determines if the O2S 1 is functioning properly by checking for an adequate number of O2S 1 voltage transitions above and below the bias range of 300-600 millivolts. This Diagnostic Trouble Code (DTC) sets when the PCM fails to detect a minimum number of voltage transitions above and below the bias range during the test period.