Heated Oxygen Sensors
WARNING: This page is about a different car, the 2002 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The compuvalve monitors upstream Heated Oxygen Sensors (HO2S). The upstream HO2S is used to control engine fuel flow. The sensor detects concentration of oxygen in exhaust gas and sends a signal to PCM and to compuvalve. In a rich condition, HO2S will output a voltage of 0.6 volt or more, and in a lean condition a voltage of 0.4 volt or less will be output. In the event that HO2S fails, Malfunction Indicator Light (MIL) will be illuminated.