System Overview

The ECM monitors engine and transmission operation and contains a self-diagnostic system which stores diagnostic trouble code(s). Models utilize On-Board Diagnostics Generation II (OBD-II) standards. Federal law mandates this type of diagnostic system for all vehicles by 1996.

The goal of OBD-II regulation is to provide the vehicle with an on-board diagnostic system which is capable of continuously monitoring the efficiency of emissions control system, and to improve diagnosis and repair when system failures occur.

The Federal Test Procedure (FTP) sets maximum allowable emission standards. A Malfunction Indicator Lamp (MIL) must illuminate if a system or component either fails or deteriorates to a point where the vehicle emissions could rise above 1 1/2 times FTP standards.

If malfunction does not reoccur in 3 trips, the MIL goes off, but diagnostic trouble codes remain recorded in ECM memory. Trouble codes may only be retrieved using an appropriate scan tool or Toyota/Lexus scan tool connected to new standardized Data Link Connector (DLC). The scan tool also provides freeze-frame data and can be used to clear codes.