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. Since the various components need to be monitored during different driving conditions, the OBD II system is designed to run separate monitoring programs called Readiness Monitors. Many state emissions inspection and maintenance (I/M) programs require that vehicles complete their Readiness Monitors before beginning an emissions test. See OBD MONITOR & DRIVE CYCLE PATTERNS  specific to this vehicle.

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 is displayed as an engine icon on gauge cluster on instrument panel. 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. DTCs may be retrieved using an OBD-II scan tool that complies with SAE standard J-1978, SAE standard J-1979 or Toyota hand-held tester connected to Data Link Connector No. 3 (DLC3). 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 .