If the oxygen sensor is working properly, but its signal voltage is not normal, make sure that the fuel mixture control system is not malfunctioning as follows:
- injector malfunction;
- air leak in the intake manifold;
- malfunction of the mass air flow sensor, the purge valve of the adsorber and the coolant temperature sensor;
- wiring fault.
Note. When the accelerator pedal is suddenly released after the engine has been running at about 4000 rpm⁻¹, the fuel supply is briefly interrupted and the HI-SCAN device shows values no higher than 200 mV. When the accelerator pedal is pressed sharply, the readings will go into the range of 600–1000 mV. When the speed drops to idle, the signal voltage will fluctuate between the intervals of 200 mV and 600–1000 mV. In this case, the oxygen sensor can be considered serviceable.