Circuit Description

PCM provides about 0.45 volt reference to HO2S 1. HO2S 1 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 1 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 ECT, IAT, MAF, MAP or TP sensor DTCs set.
• No EVAP system DTC set.
• No fuel injector circuit, fuel trim, misfire or transaxle DTCs set.
• MAF less than 24 grams per second.
• ECT and IAT less than 95°F (35°C) at start-up.
• Difference between ECT and IAT not greater than 11°F (6°C).
• HO2S 1 voltage remains within 0.15 volt of bias voltage for longer amount of time than it should.
• Average mass airflow for sample period is less than 18 gm/s.