Overview of On-Board Diagnostics & NLEV Program

OVERVIEW OF ON-BOARD DIAGNOSTICS (OBD 1 & 2)

In continuing efforts to improve air quality, the Environmental Protection Agency (EPA) amended the Clean Air Act in 1990. The Clean Air Act was originally mandated in 1970. The Clean Air Act has a direct impact on automobile manufactures whereby they are responsible to comply with the regulations set forth by the EPA. The 1990 amendment of the Clean Air Act set forth all of the changes currently being introduced on vehicles sold in the United States today.

In 1967, the State of California formed the California Air Resources Board (CARB) to develop and carry out air quality improvement programs for California's unique air pollution conditions. Through the years, CARB programs have evolved into what we now know as ON Board Diagnostics (OBD) and the National Low Emission Vehicle Program.

The EPA has adopted many of the CARB programs as National programs and laws.

One of these earlier programs was OBD I and the introduction of the "check engine"light.

BMW first introduced OBD I and the check engine light in the 1987 model year. This enhanced diagnosis through the display of "flash codes" using the check engine light as well as the BMW 2013 and MODIC. OBD I was only the first step in an ongoing effort to monitor and reduce tailpipe emissions.

By the 1989 model year all automotive manufactures had to assure that all individual components influencing the composition of exhaust emissions would be electrically monitored and that the driver be informed whenever such a component tailed.

Since the 1996 model year all vehicles must comply with OBD II requirements. OBD II requires the monitoring of virtually every component that can affect the emission performance of a vehicle plus store the associated fault code and condition in memory.

If a problem is detected and then re-detected during a later drive cycle more than one time, the OBD II system must also illuminate the Check Engine Light in the instrument cluster to alert the driver that a malfunction has occurred. However; the flash code function of the Check Engine Light in OBD I vehicles is not a function in OBD II vehicles.

This requirement is carried out by the Engine Control Module (ECM/DME) as well as the Automatic Transmission Control Module (EGS/AGS) and the Electronic Throttle Control Module (EML) to monitor and store faults associated with all components/systems that can influence exhaust and evaporative emissions.

Overview of the National Low Emission Vehicle Program

Emission Reduction Stages:

While OBD II has the function of monitoring for emission related faults and alerting the operator of the vehicle, the National Low Emission Vehicle Program requires a certain number of vehicles produced (specific to manufacturing totals) currently comply with the following emission stages;

TLEV: Transitional Low Emission Vehicle

LEV: Low Emission Vehicle

ULEV: Ultra Low Emission Vehicle.

Prior to the National Low Emission Vehicle Program, the most stringent exhaust reduction compliancy is what is known internally within BMW as HO II. The benefit of exhaust emission reductions that the National Low Emission Vehicle Program provides compared with the HO II standard is as follows:





TLEV- 50% cleaner.

LEV- 70% cleaner.

ULEV- 84% cleaner.




OBD II Tailpipe Compliance




OBD II Evaporative Emission Compliance