Light Off Catalyst
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2002 Mercury Sable, 2002 Mercury Mountaineer, 2002 Mercury Grand Marquis, 2002 Mercury Cougar, and 2002 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.