Oxygen Sensor Control, Checking

Oxygen sensor control, checking

Function of oxygen sensor control

The oxygen sensors compare the oxygen content in the air with the residual oxygen content in the exhaust gas and send a voltage signal to the control module.

The voltage signal for "Mixture too rich" (low residual oxygen) is between about 0.5 and 1.0 V (relative to reference Ground (GND)).

The voltage signal for "Mixture too lean" (high residual oxygen) is between about 0 and 0.5 V (relative to reference Ground (GND)).

The transition from "rich" to "lean" is accompanied by a voltage jump from between 0.5 and 1.0 V to between 0 and 0.5 V (relative to reference Ground (GND)), and vice versa (lamda = 1.0).

Because of the sharp voltage jump the oxygen sensor control cannot maintain a constant ideal mixture composition of lamda = 1.0. The system fluctuates continuously between "slightly too lean" and "slightly too rich".

NOTE: Reference Ground (GND) = preset Ground (GND) from Engine Control Module (ECM).

If the voltage does not change or only changes slowly the following malfunctions are possible:
- Slits or holes in probe head are blocked.
- Oxygen sensor has been subjected to excessive thermal stress.
- Contact resistance in signal wire or Ground (GND) wire.
- Oxygen sensor too cold; sensor heater not working.
- Oxygen sensor damaged by contact spray or similar product. (The contact spray is drawn through the fine cavities in the electrical wiring as a result of thermal fluctuations and capillary effect.)
- Oxygen sensor damaged by silicone vapors. (The engine draws in traces of any silicone-based sealants that may have been used. The silicone does not burn and damages the oxygen sensor.)