Oxygen Sensor: Description and Operation

PURPOSE
The Engine Control Module (ECM) uses the O2 signal to fine tune the Fuel Injector duration to maintain the correct fuel mixture.

OPERATION
The Oxygen Sensor is mounted to the Exhaust Manifold or pipe with the sensor end extending into the exhaust stream. It uses zirconia and platinum to compare exhaust oxygen content with that of the outside air.
When heated by the combination of its internal heater and exhaust gases, the sensor supplies a low voltage signal (0.0 - 1.0 volt) to the ECM. The amount of voltage produced is determined by the air/fuel mixture, A high voltage (0.7 - 1.0 volt) indicates a rich mixture, and a low (0 - 0.3 volts) voltage indicates a lean mixture.

Oxygen sensor operation is monitored by the Engine Control Module (ECM) and a malfunction should be accompanied by a Diagnostic Trouble Code (DTC). Circuit and output testing procedures are covered in detail in the Diagnostic Trouble Code Charts. Testing and Inspection

By controlling the air/fuel ratio with a Primary HO2S (Sensor 1) and a Secondary HO2S (Sensor 2), the deterioration of the Primary HO2S (Sensor 1) can be evaluated by its feedback period. When the feedback period of the HO2S exceeds a certain value during stable driving conditions, the sensor will be judged as deteriorated. When deterioration has been detected during two consecutive trips, the MIL comes on and DTC P0133 will be stored.
NOTE: If DTC P0131, P0132 and/or P0135 are stored at the same time as DTC P0133, troubleshoot those DTCs first, then troubleshoot DTC P0133.


HINT: When monitoring oxygen sensor operation with an oscilloscope, watch for a sine wave with a frequency of at least 8 cycles in 10 seconds. A "lazy" oxygen sensor will not always set a code, but will usually cause abnormal emissions levels.