Monitor Description
WARNING: This page is about a different car, the 2006 Lexus RX 400h. However, it is still accessible from the selected car via links, so may be relevant.
5 hours after the engine switch is turned off, the soak timer activates the ECM (included in the HV Control ECU) to begin the EVAP system monitor. While the engine is running, the ECM monitors the synchronization of the soak timer and the CPU clock. If these two are not synchronized, the ECM interprets this as a malfunction. The ECM illuminates the MIL and sets the DTC (2 trip detection logic).