Oxygen Sensor: Description and Operation

OXYGEN SENSOR DIAGNOSIS
Diagnose the fuel control HO2S for the following conditions:
^ Heater performance, time to activity on cold start
^ Slow response
^ Response time, time to switch R/L or L/R
^ Inactive signal, output steady at bias voltage - approximately 450 mV
^ Signal fixed high
^ Signal fixed low

Diagnose the catalyst monitor HO2S for the following functions:
^ Heater performance, time to activity on cold start
^ Signal fixed low during steady state conditions
^ Inactive sensor

HEATED OXYGEN SENSORS
The main function of the pre-catalyst heated oxygen sensor (HO2S) is to provide the powertrain control module (PCM) with exhaust stream information in order to maintain proper fueling to hold emissions within acceptable levels. These oxygen sensors are always located between the exhaust manifold and the catalytic converter. After the sensor reaches the operating temperature, the sensor generates a voltage inversely proportional to the amount of oxygen present in the exhaust gases.

The PCM uses the signal voltage from the fuel control HO2S in a Closed Loop in order to adjust the fuel injector pulse width. While in a Closed Loop, the PCM can adjust fuel delivery in order to maintain an air to fuel ratio which allows the best combination of emission control and driveability.

If the oxygen sensor pigtail wiring, connector, or terminal are damaged, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, the connector, or the terminals. In order for the sensor to function properly, the sensor must have a clean air reference provided to the sensor. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors, or terminals could result in the obstruction of the air reference. Any attempt to repair the wires, connectors, or terminals could degrade oxygen sensor performance.