Open Loop Mode

During start-up and acceleration, the EFC controller disregards any oxygen sensor signals. This results in temporarily richer mixtures for better performance. During warm-up, the air injection system supplies air to the exhaust manifold (ahead of both converters). This additional air allows complete oxidation of HC and CO in the main converter during this rich mixture period (NOx is not a factor since low temperatures do not create this emission). This "burning" helps quickly raise exhaust system temperatures, allowing the oxygen sensor and 3-way catalyst to warm-up faster.

At normal operating temperatures, the air switching valve in the air injection system directs additional air from the exhaust ports to the exhaust pipe, just ahead of the oxidation catalyst. The Closed Loop Mode comes into operation.