Light Off Catalyst
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2003 Mercury Sable, 2003 Mercury Mountaineer, 2003 Mercury Marauder, 2003 Mercury Grand Marquis, and 2003 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
As the catalyst heats up, converter efficiency rises rapidly. The point at which conversion efficiency exceeds 50 percent is called catalyst light off. For most catalysts this point occurs at 475-575°F (246-301°C). A fast light catalyst is a 3-Way Catalyst (TWC), that is located as close to exhaust manifold as possible. Because light off catalyst is located close to exhaust manifold it will light off faster and reduce emissions quicker than the catalyst located under vehicle. Once catalyst lights off, the catalyst will quickly reach maximum conversion efficiency.