Oxygen Sensor (O2S)
With engine at normal operating temperature, unplug connector from O2S. Measure voltage between O2S terminal and ground. Voltage should increase with increasing engine speed, and decrease with decreasing engine speed. Voltage at idle should fluctuate within a range of 0.2-0.8 volt.
NOTE:
A steady voltage of more than 0.55 volt indicates a continuously rich condition. A steady voltage of less than 0.55 volt indicates a continuously lean condition.