Self Diagnostic System: Introduction
ECM monitors engine and transmission operation and contains a self-diagnostic system which stores DTCs. A Malfunction Indicator Light (MIL), also called CHECK ENGINE light, located on instrument panel, will illuminate if a system or component fails and sets a DTC.
MIL illuminates with ignition switch in ON position, engine off. Once engine is started, MIL should go off. If MIL remains illuminated, ECM has detected a malfunction or abnormality in system. If MIL does not illuminate, inspect circuit.
If malfunction does not reoccur in 3 trips, MIL goes off, but DTC remains stored in ECM memory. DTCs may only be retrieved using an appropriate OBD-II scan tool or Toyota scan tool connected to 16-pin Data Link Connector (DLC3), located at lower left corner of instrument panel or below parking brake handle. See Fig 1 and Fig 2 . Scan tool provides freeze-frame data and can be used to clear DTCs.
ECM records engine operating condition (fuel system, calculated load, coolant temperature, fuel trim (mixture), engine speed, vehicle speed, etc.) with first malfunction ONLY. Information is ONLY for 1st recorded failure, even if more than one DTC has been recorded. Freeze-frame data is only updated when all DTCs have been cleared, or a misfire or fuel-trim malfunction has occurred.