Circuit Description

This test is used to determine if the heating element in the front oxygen sensor is operating properly. The sensor acts as a battery because it creates its own voltage once it reaches operating temperature. This voltage is produced when the oxygen content in the exhaust stream is different than that in the atmosphere.

Heating element is energized through the ignition circuit when ignition is on, allowing sensor to reach operating temperature quickly. This in turn allows PCM to enter into "closed loop" quicker.

When cold, the voltage that the PCM measures on the oxygen sensor high and low input circuits is called bias voltage. If it takes too long for oxygen sensor to vary the bias voltage within a specific time since ignition was turned on, DTC will set.