Circuit Description

VCM provides about 0.45 volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. When ignition is turned on, battery voltage is supplied to HO2S heater to provide for faster sensor warm-up, thus allowing sensor to become active in a shorter period of time. VCM reads amount of time necessary for sensor to become active after start-up.

Conditions for setting DTC:

• MAF less than 27 gm/s.
• Engine running greater than 2 seconds.
• ECT and IAT less than 89.6°F (32°C).
• Difference between ECT and IAT not greater than 41°F (5°C).
• Elapsed time HO2S bias voltage is greater than predetermined value.