California Models

PURPOSE
The Sequential Multiport Fuel Injection System on this vehicle uses three Heated Oxygen Sensors (HO2S) (two main and one sub) to monitor the oxygen content of the exhaust gases. The Engine Control Module (ECM) uses the voltage signal from the Heated Oxygen Sensors to assist in determining proper Air / Fuel mixture to maintain optimum performance and economy in all driving conditions. The Sub Heated Oxygen (SHO2) Sensor is mounted after the Three Way Catalytic Convertor and is used to measure the effectiveness of the Convertor by comparing readings with the exhaust gas measured upstream.

OPERATION
A measureable voltage is generated by comparing the amount of oxygen in the exhaust gas with the amount in the ambient air. The HO2S operates only within a certain temperature range of approximately 285 - 850°C (545 - 1530°F). The exhaust gases reach the outer surface of the HO2S tip via the openings in the protective sleeve. Ambient air reaches the sensor's inner surface via channels. The difference in oxygen content produces a voltage read by the ECM. The heating element within the HO2S is controlled by the ECM. When the sensor is cold the ECM grounds the circuit, causing the sensor to heat. The electric heater allows the sensor to reach operating temperature much sooner than it could simply by using exhaust gas to heat it. The heater also prevents sensor cool-down during periods of extended idling.