Two-Trip Detection Logic
WARNING: This page is about a different car, the 1997 Lexus SC 300. However, it is still accessible from the selected car via links, so may be relevant.
When a malfunction initially occurs, Diagnostic Trouble Code (DTC) will be temporarily stored in ECM memory, but MIL on instrument panel will not illuminate. The second time that a malfunction is detected, MIL on instrument panel will illuminate, provided ignition is turned off and then back on after first malfunction was detected. This is referred to as the 2-Trip Detection Logic and only applies to specified DTCs. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION table under SELF-DIAGNOSTIC SYSTEM.
NOTE:
When road testing vehicle in CHECK mode (Lexus scan tool only), the Two Trip Detection Logic will not function. Also, MIL will illuminate first time a malfunction is detected.