Oxygen Sensor: Description and Operation

Exhaust Oxygen Sensor (02):

PURPOSE
The oxygen sensor, installed in the exhaust manifold, monitors exhaust gas oxygen content and produce a voltage output. The control module uses this voltage value to calculate the percentage of oxygen in the exhaust gas and adjusts the fuel injector pulse width to maintain the correct air/fuel ratio.

CONSTRUCTION AND OPERATION
The sensor consists of a hollow Zirconia element with a Platinum coating on its inside and outside surfaces. The open end of the element is exposed to the atmosphere and its surface is connected to the control module, while the closed end protrudes into the exhaust stream and its surface is connected to ground. The oxygen sensor element only reacts efficiently with oxygen if the temperature of the element is around 300°C (575°F) or hotter. When there is a difference in the amount of oxygen reacting with the inner and outer surfaces, a voltage potential is generated. The normal operating voltage range is approximately 0.1-1.0V. Voltage increases when the concentration of oxygen in the exhaust is low (rich air/fuel ratio) and decreases when the concentration is high (lean air/fuel ratio).

Oxygen Sensor Output Voltage vs. Air/Fuel Ratio:

The difference in oxygen concentration in the narrow range of optimum air/fuel ratio causes a large voltage change that is easily measured.

HEATED OXYGEN SENSOR TYPE
The heated oxygen sensor works in the same manner as the non-heated oxygen sensor. The exception is that B+ is supplied to a heating element that is part of the sensor itself. The heater helps the control module control the fuel injection sooner for better fuel emissions. There are no Diagnostic Trouble Codes (DTC's) to detect if the heater part of the sensor is working. To check the heater, REFER TO COMPUTERS AND CONTROL SYSTEMS/DIAGNOSIS AND TESTING PROCEDURES/OXYGEN SENSOR TESTING.


CONDITIONS THAT CAN SET CODES
An open O2 sensor, should set a Diagnostic Trouble Code (DTC) 13. A constant low voltage in the O2 sensor circuit should set a DTC 44. A constant high voltage in the circuit should set a DTC 45. DTC 44 and DTC 45 could be set as a result of fuel system problems. REFER TO COMPUTERS AND CONTROL SYSTEMS/DIAGNOSTIC CHARTS for diagnosis of these codes.