Oxygen Sensor (O2S) Control, Checking

Oxygen Sensor (O2S) Control, Checking


NOTE:
- The oxygen sensor compares the oxygen content of the outside air with the residual oxygen content in the exhaust gas, and generates a voltage input signal to the Engine Control Module (ECM).
- The voltage signal for a "rich" mixture (little residual oxygen content) is approx. 0.7 - 0.9 volts.
- The voltage signal for a "lean" mixture (high residual oxygen content) is approx. 0 - 0.2 volts.
- Because oxygen sensors are insulated from engine ground, negative current flow may occur.
- During the transition from "rich" to "lean" mixture (Lambda = 1.0), voltage fluctuates between 0.7 - 0.9 volts and 0 - 0.2 volts, and vice versa.
- Because of the abrupt voltage changes, the ECM cannot continuously maintain the ideal fuel/air mixture (Lambda = 1.0). Oxygen sensor control is continuously changing between conditions that are slightly too lean and slightly too rich

If oxygen sensor voltage does not fluctuate, the sensor does not respond, or responds too slowly, the following causes are possible:
- Slits in the oxygen sensor tip are plugged
- Sensor not up to operating temperature (cold-start)
- Sensor has been thermally overloaded
- Transition resistance in signal wire or reference Ground connection
- Sensor has been damaged by electrical contact cleaner or similar contaminant (drawn through signal wire by capillary action due to thermal fluctuation).
- Sensor has been damaged by exposure to silicone. When using silicone sprays and sealants, silicone residue is drawn into the engine where it passes unburned into the exhaust and can damage the oxygen sensor.