Circuit Description

PCM 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. PCM reads amount of time necessary for sensor to become active after start-up.

Conditions required to set DTC are:

• No CKP, ECT, EGR pintle position, IAT, MAF, MAP or TP sensor DTCs set.
• No EVAP system DTC set.
• No fuel injector circuit, fuel trim or misfire DTCs set.
• ECT and IAT less than 90°F (32°C) at start-up.
• Difference between ECT and IAT no greater than 14°F (8°C).
• Ignition voltage is 10-18 volts.
• MAF less than 15 grams per second during sample period.
• HO2S 1 voltage remains within 0.15 volt of bias voltage (0.40-0.50 volt) for longer amount of time than it should.