California Models

PURPOSE
Two oxygen sensors, a main and and a sub, measure the oxygen content in the exhaust and send a voltage signal to the ECU.

LOCATION
The oxygen sensors are mounted in the exhaust, the main sensor in the rear exhaust manifold and the sub after the catalyst.

CONSTRUCTION
Each sensor consists of a steel housing, sensor tip, and its protective sleeve. The sensor tip itself is made from a platinum covered zirconium-oxide pipe. The main sensor also contains a heating element.

OPERATION
A measureable voltage is generated by comparing the amount of oxygen in the exhaust gas with the amount in the ambient air.

The sensor operates only within a certain temperature range of approx. 545 - 1530°F (285 - 850°C).

The exhaust gases reach the outer surface of the oxygen sensor tip via the openings in the protective sleeve. Ambient air reaches the sensor's inner surface via channels. The differance in oxygen content produces a voltage read by the ECU.

The heating element is controlled by the ECU. When the sensor is cold the ECU 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.