What is OBD II?
OBD II is an acronym for On-Board Diagnostics II, the second generation
of on-board self-diagnostic equipment requirements for
light- and medium-duty California vehicles. On-board diagnostic capabilities are incorporated
into the hardware and software of a vehicle's on-board computer to
monitor virtually every component that can affect emission performance.
Each component is checked by a diagnostic routine to verify that it is
functioning properly. If a problem or malfunction is detected, the OBD
II system illuminates a warning light on the vehicle instrument panel
to alert the driver. This warning light will typically display the
phrase "Check Engine" or "Service Engine Soon," and will often include
an engine symbol. The system will also
store important information about any detected malfunction so
that a repair technician can accurately find and fix
What was OBD I?
On-Board Diagnostics I (OBD I) was California's first OBD regulation
which required manufacturers to monitor some of the emission control
components on vehicles. Required starting with the 1988 model year, OBD
systems were not fully effective because they were limited to
monitoring only a few of the emission-related components, and the
not calibrated to a specific level of emission performance. OBD II was
developed to address these shortcomings and make the system
more powerful and user-friendly for service technicians.
Why is OBD II
Even though new vehicles sold in California are the cleanest in the
world, the millions of cars on the road and the ever increasing miles
they travel each day make them our single greatest source of smog
forming emissions. While the new vehicles in California may start out
with very low emissions, improper maintenance or faulty components can
cause vehicle emission levels to sharply increase.
estimate that approximately 50% of the total emissions from late-model
vehicles are excess emissions, meaning that they are the result of
emission-related malfunctions. OBD II works
to ensure that the vehicles remain as clean as possible over
their entire life.
Does my car have
All 1996 and newer model year gasoline and alternate fuel passenger
trucks are required to have OBD II systems. All 1997 and newer
model year diesel fueled passenger cars and trucks are also required to
OBD II requirements. Additionally, a small number of 1994 and
1995 model year gasoline vehicles were equipped with OBD II
systems. To verify that your vehicle is equipped with OBD II,
you can look for the words "OBD II" on the emission control information
label attached to the underside of the vehicle hood.
Do other states
require OBD II?
Yes. The United States Environmental Protection Agency (U.S. EPA)
all 1996 and newer model year passenger cars and trucks sold
in any state to meet the U.S. EPA
OBD requirements. While U.S. EPA's OBD requirements differ slightly
from California's OBD II requirements, systems
designed to meet California's requirements are also accepted
by U.S. EPA as meeting the federal requirements. In practice,
virtually all vehicles sold in the U.S. are designed and certified to
meet California's OBD II requirements, regardless of where in the U.S.
they are sold.
More information about U.S. EPA's OBD requirements can be found at the U.S. EPA OBD website.
What should I do if
the warning light comes on?
Most manufacturers advise having the vehicle serviced as soon as
conveniently possible. Since there are many different problems that can
cause the light to illuminate, it is hard to generalize how severe a
problem may be. However, the problem will often cause a
noticeable effect on fuel economy, performance,
or the driveability of your vehicle, and extended driving without
fixing the problem could possibly lead to damage of other components.
Additionally, there are certain malfunctions that can cause the warning
light to blink. This indicates that a malfunction is occurring
that could be damaging your catalytic converter. Because
replacement of the catalyst can be expensive, many manufacturers
recommend having the vehicle serviced as soon as possible if the
warning light is blinking.
Does the warning
light only mean the emissions controls on my car aren't working?
While all malfunctions that cause the light to illuminate either affect
emissions or the ability of the OBD system to work properly,
many also can affect fuel economy, and several can
cause driveability problems or a decrease in overall
performance. Manufacturers generally optimize their vehicles for
performance, fuel economy, and emissions. As such, virtually any
malfunctioning component can result in the vehicle running in a
condition that is less than optimal.
Do I have to go to
the dealer to get my OBD II car fixed?
No. Properly trained and equipped independent shops are capable of
utilizing the diagnostic information from the OBD II system
and can make repairs just like dealers. In fact,
several of the provisions incorporated in the OBD II regulation are
intended to make it easier for independent shops to diagnose
and repair vehicles accurately and in a cost-effective manner.
It should be noted, however, that California's
warranty requires the vehicle manufacturer to repair under warranty any
problem that the OBD II system detects if the vehicle is less
than 3 years old and has less than 50,000 miles. Manufacturers
only authorize their dealers to perform warranty work. Further,
components which exceed a defined cost limit
at the time the vehicle was produced (currently about $600) are
covered for 7 years or 70,000
miles - this list of covered parts, which varies from car to
car, should be listed in the owner's manual or accompanying
that came with the vehicle. Additionally, if you have
a vehicle that is certified by ARB as a partial zero emission vehicle
(PZEV), any problem detected by the OBD II system is covered under
warranty as long as the vehicle is less than 15 years old and has less
than 150,000 miles. Starting with the 2018 model year, you can purchase
a vehicle certified by ARB as a transitional zero emission vehicle
(TZEV), which also will be covered under warranty for 15 years or
150,000 miles. The "energy storage device" (i.e., the hybrid battery)
on PZEVs and TZEVs are covered under warranty for 10 years.
of vehicles that
are certified as PZEVs and TZEVs
can be found at ARB's Drive
Clean website (select vehicles with a Smog Rating of 9 to
PZEVs and TZEVs).
How is Smog Check
affected by OBD II?
In California, technicians
are required to perform an OBD II check (visual and
functional) during the Smog Check inspection. Specifically,
the technician visually checks to make sure the warning light is
functional, and then the Smog
Check test equipment communicates with the on-board computer for fault
information. If a fault is currently causing
the light to
be on, you need to have the malfunctioning component
repaired before you can pass the inspection.
Additionally, the vehicle stores information known as "readiness
indicators" to indicate if the vehicle is ready for an inspection. If
too many readiness indicators are "incomplete," the vehicle will fail
inspection because it means that the vehicle has not
been operated enough since the on-board memory was last cleared to
of the OBD system checks to complete. This can occur if a
has recently been repaired, or if you have recently
a dead, disconnected, or replaced battery. It does not necessarily mean
that anything is
wrong with your car - it simply means that the vehicle hasn't had a
chance to run all of its self-diagnostics to confirm that everything is
okay. The vehicle will need
to be driven more before the vehicle can be tested
to pass. Vehicle owners who fail Smog Check due to
incomplete readiness indicators should drive their vehicle as they
do for about a week or so to set these readiness indicators to
If the incomplete readiness indicators were most likely not a
result of a recently disconnected/replaced vehicle battery, or if the
vehicle is not driven regularly, the
vehicle owner may wish to seek repair technician help in setting readiness.
The technician can access technical information from the vehicle manufacturer and should be able to advise the owner of specific
driving patterns needed to set the indicators, or may be able to
operate the vehicle (most likely on a dynamometer in the shop)
set the monitors. The technician will have access to a scan tool
to determine which monitors have not completed.
Smog Check inspections
for 2000 and newer model year vehicles are now primarily based on an
inspection of the OBD II system; tailpipe testing is no longer
required. 1996 through 1999 model year gasoline vehicles receive both an OBD
inspection and tailpipe testing. In addition, 2000 through 2007 model
year medium-duty vehicles (vehicles with a gross vehicle weight rating
between 8,500 and 14,000 lbs.) with federal-only certified OBD systems
may require both an OBD inspection and tailpipe test.
More detailed information about
California's current OBD
II-based Smog Check program can be found at BAR's
Does OBD II prevent
me from using non-OEM parts or modifying my car?
No. Aftermarket parts manufacturers continue
produce replacement parts to fit most vehicles. These parts
are required to be
functionally equivalent to the original equipment manufacturer (OEM) parts and are, therefore, compatible
with the vehicle's OBD II system. For add-on or
performance enhancing parts, aftermarket manufacturers
are required to obtain an exemption
from ARB before legally offering such parts for sale in
California. The process requires the aftermarket manufacturers to
demonstrate that their products are compatible with vehicle OBD II
systems. Parts that
been granted such approval can be found at ARB's aftermarket
Vehicle owners should make sure add-on and modified powertrain products
have a valid Executive Order from ARB that permits their use on
California registered on-road vehicles before installing such products.
If I need to
replace the catalyst (or catalytic converter) on my OBD II car, can I
use any catalyst that is available?
California has specific regulations defining minimum
performance levels for catalysts on all cars, including those that are
OBD II-equipped. Replacement catalysts available from the dealer for
your specific vehicle are legal. Additionally, aftermarket
catalysts that have been approved by ARB are legal for use on cars in
California. If you are purchasing a new catalyst for your OBD
II vehicle, you need to make sure it is approved by ARB for use on your
specific vehicle. Approved aftermarket catalytic converters
can be found on ARB's aftermarket
The aftermarket catalyst manufacturers also have catalogs or online
resources that identify which catalysts are approved for
specific vehicles in California.
How much do OBD II
systems add to the cost of a new car?
In most cases, equipping a new vehicle with an OBD II system has only
required minimal additional hardware, resulting in only slight
additional costs. This is because most OBD II requirements can
met by only adding new software in the vehicle's
computer. In 1996, the federal government estimated that the OBD II
requirements increased the retail cost of a 1996 model year new vehicle
by an average of $61. Overall, OBD II is anticipated to
in cost-savings to the consumer by catching faults quickly
(before other components can be damaged) and by pinpointing the source
of the fault to aid technicians in making fast,
What is OBD III?
OBD III is a term used to describe the concept of "remote OBD."
Under this concept, vehicle would have the ability to transmit OBD
fault information to roadside receivers, for example, through cellular
networks. The benefit of such a concept is that a motorist would not
have to take their vehicle to a station for an emissions inspection as
long as the vehicle is communicating that there are no active
emission-related malfunctions. If the OBD II system has
problem, the vehicle owner would be expected to have the problem
repaired in a timely fashion. Correction of the problem would
verified through the OBD data transmitted after the vehicle has been
California has not adopted any kind of
mandatory remote OBD program at this time. The remote OBD concept has been
studied by states, including California, through pilot programs that
are based on voluntary participation. ARB's OBD II regulation does not
require manufacturers to equip vehicles with the ability to wirelessly
transmit OBD information. Vehicles typically must be retrofitted with
equipment that can transmit the OBD data in order to participate.
Overall, the potential benefits of the remote OBD concept are added
convenience and reduced inspection costs to owners of vehicles that are
in proper operating condition and greater emission reductions from the
more rapid identification and repair of emission-related malfunctions
when they do occur.