Circuit Description
WARNING: This page is about a different car, the 2003 Toyota Matrix and 2003 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.
Battery positive voltage is applied to terminal BATT of ECM even when ignition switch is OFF for use by DTC memory and air-fuel ratio adaptive control value memory, etc. Detecting condition of DTC is when there is an open in back up power source circuit. If DTC P1600 is displayed, ECM does not store another DTC.