Camry 2.4L (PZEV)
WARNING: This page does not describe the selected car, but rather 17 other vehicles, including the 2003 Toyota Tundra, 2003 Toyota Tacoma, 2003 Toyota Sienna, 2003 Toyota Sequoia, and 2003 Toyota RAV4. However, it is still accessible from the selected car via links, so may be relevant.
The Toyota-HCAC (Hydrocarbon Absorptive Catalyst) system has been adopted in the rear TWC. See Fig 1.
The Toyota HCAC (Hydrocarbon Adsorptive Catalyst) system has been adopted in the rear TWC. In this TWC, the bottom layer, closest to the ceramic, is coated with HC adsorbent, and the layer above is coated with a three-way catalyst. When the TWC is not activated immediately, as when a cold engine is started, the HC adsorbent layer temporarily adsorbs the discharged HC. As the TWC becomes activated, it gradually purifies the stored HC.