System Overview

The ECM monitors engine operation and contains a self-diagnostic system which stores Diagnostic Trouble Codes (DTCs) and complies to 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 vehicle with an on-board diagnostic system which is capable of continuously monitoring the efficiency of emission 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 Light (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 ignition cycles, the MIL goes off, but DTCs remain recorded in ECM memory. DTCs may only be retrieved using an On-Board Diagnostic (OBD-II) scan tester that complies with SAE standard J-1978 or Lexus scan tester connected to new standardized Data Link Connector (DLC) No. 3. The scan tester also provides freeze-frame data and can be used to clear codes.