Circuit Description

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 is 10-18 volts.
• MAF calculated airflow is less than 18 grams per second.
• HO2S 2 voltage remains within 0.15 volt of bias voltage (.40-.50 volt) for longer amount of time than it should.