If the oxygen sensor is OK, but its signal voltage is not correct, check for the following malfunctions in the mixture control system:
- injector malfunction;
- air leakage into the intake pipeline;
- malfunction of the mass air flow sensor, adsorber purge valve and coolant temperature sensor;
- wiring fault.
Note. When the accelerator pedal is suddenly released after the engine is running at a crankshaft speed of about 4000 min-1, the fuel supply stops briefly and the HI-SCAN device shows values not higher than 200 mV. With a sharp press on the accelerator pedal, the readings will go into the range of 600-1000 mV. When the speed drops to idle, the signal voltage will fluctuate between 200 mV and 600-1000 mV intervals. In this case, the oxygen sensor can be considered serviceable.