System Overview

Engine Control Module (ECM) monitors engine operation and contains a self-diagnostic system which stores Diagnostic Trouble Codes (DTC) and complies to On-Board Diagnostics Generation II (OBD-II) standards.

Self-diagnostic system is used to provide vehicle with an on-board diagnostic system which is capable of continuously monitoring efficiency of emission control system, and improving diagnosis and repair when system failures occur.

OBD-II regulations require that Malfunction Indicator Light (MIL) must be illuminated when a malfunction exists in the emission control system which affects vehicle emissions or a malfunction exists in the ECM. MIL may also be illuminated when a DTC is stored in the ECM memory due to a system or component failure. MIL may be illuminated when no DTCs are stored in ECM but a problem exists in the Hybrid Vehicle (HV) control system. MIL is located on instrument cluster at center of instrument panel and is displayed as an engine icon. MIL may also be referred to as CHECK ENGINE light.

If malfunction does not reoccur in 3 consecutive trips, MIL will turn off, but DTCs remain stored in ECM memory. When DTC P3190 or P3191 are stored due to a low-fuel condition, the ECM illuminates the MIL. After the next trip when ECM determines that a low-fuel condition no longer exists, it turns off the MIL, but DTC will remain stored in the ECM memory. DTCs may be retrieved using an OBD-II scan tool that complies with SAE standard J-1978 or Toyota hand-held tester connected to Data Link Connector (DLC) No. 3. Scan tool or Toyota hand-held tester may also be used to provide freeze frame data and to clear DTCs from ECM. For additional information on freeze frame data, see FREEZE FRAME DATA .