OBD II Overview
OBDII (On Board Diagnostics II) systems are required by Federal
law on all passenger cars and light trucks manufactured
since 1996. It is a computer on board the vehicle that
monitors the engine and emission control equipment to verify
that all systems are working properly. If the monitor detects
a fault, a code is stored in the computer, and the malfunction
indicator lamp (MIL) is illuminated.
The MIL is typically the "Check Engine" light on
the instrument panel. The MIL alerts the vehicle owner that
there is a problem and that the vehicle should be brought
in for service. The service technician can read the fault
code from the OBDII computer to help determine what repairs
OBDII converters are catalytic converters that have been
installed on vehicles with the OBDII monitoring system.
All 1996 and newer passenger cars and light trucks are OBDII
vehicles. Some 1994 and 1995 vehicles also have an OBDII
system, because the implementation of the law was phased
The most reliable way to identify whether or not a vehicle
is an OBDII vehicle is by visual inspection of the exhaust
system. If there is an oxygen sensor installed anywhere downstream
of a catalytic converter, then it is an OBDII vehicle. Some
manufacturers state whether a vehicle is OBDII compliant
on the emissions label located in the engine compartment.
The OBDII system is required to monitor the catalytic converter
to ensure that the tailpipe emissions do not exceed the legal
limits. Unfortunately, there is no current emission sensor
technology available that can be installed on a vehicle to
monitor tailpipe pollutant levels. Instead, vehicle manufacturers
use an oxygen sensor to indirectly estimate whether or not
a catalytic converter is functioning properly.
Since emission levels are estimated rather than being measured
directly, it is theoretically possible to produce a catalytic
converter which meets emission standards yet also shows a "check
engine" light on the instrument panel.
Therefore, government policy needs to ensure that aftermarket
catalytic converters are compatible with the vehicle's OBDII
system, in addition to meeting emission requirements. The
United States Environmental Protection Agency and the California
Air Resources Board have implemented policies to address
this issue. However, they have taken two different approaches
to the problem.
Obviously, this is a relatively complicated set of parameters
for a repair technician to consider when trying to decide
which converter to install on a vehicle. As a result, California
OBDII converters may not be selected simply by referring
to a vehicle engine size and weight. The California Air Resources
Board requires OBDII converters to cataloged specifically
by vehicle make, model, engine, and any further description
needed to precisely characterize an approved vehicle application.
Repair technicians may only install the converter that is
cataloged for the vehicle, and may not install a converter
on any vehicle that is not listed.
Converters are designed to meet California
OBDII requirements. A
separate application guide is available which lists California
California OBDII converter performance requires more active
catalyst with larger, more heavily loaded bricks and higher
temperature durability to meet the standards. As a result,
they have a significantly enhanced environmental impact
versus standard aftermarket converters.
This enhanced performance provides an excellent option for
environmentally conscious individuals who would like to use
CleanAir Ultra converters on pre-OBDII vehicles, or in the
other 49 states, instead of using the cheapest (and less "green")
part available. The performance enhancement of a CleanAir
Ultra converter versus a standard converter is readily observable
in I/M test lanes in side-by-side test comparisons.