Light Off Catalyst
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As the catalyst heats up, converter efficiency rises rapidly. The point at which conversion efficiency exceeds 50% is called catalyst light off. For most catalysts this point occurs between 246°C to 302°C (475°F to 575° F). A light off catalyst is a three way catalytic (TWC) converter that is located as close to the exhaust manifold as possible. Because the light off catalyst is located close to the exhaust manifold it achieves the required temperature faster and reduces emissions more quickly than the catalyst located under the body. Once the catalyst lights off, it quickly reaches the maximum conversion efficiency for that catalyst.