The most significant changes in the emission arena involve the ongoing implementation of the Clean Air Act regulations, and the changes in OBD II, which are occurring as a result of those laws. Specifically, the incorporation of OBD II testing as a part of our basic and enhanced emission testing programs will cause some controversy, but will create new service opportunities for you and me.

In should be noted that in response to its findings on OBD effectiveness and its study of the various implementation issues associated with OBD-I/M testing, EPA published a notice of proposed rulemaking (NPRM) in the Federal Register on September 20, 2000. Among other things, this notice proposes to:

1. Extend the current deadline for mandatory implementation of the OBD-I/M inspection from January 1, 2001 to January 1, 2002;

2. Clarify states' options regarding the integration of OBD-I/M checks into existing I/M networks;

3. Revise and simplify the current list of Diagnostic Trouble Codes (DTCs) that constitute the OBD-I/M failure criteria to include any DTC that leads to the dashboard Malfunction Indicator Light (MIL) being commanded on; and

4. Provide for exemptions from specific readiness code rejection criteria on OBD-equipped vehicles based upon vehicle model year. The goal of the proposed amendments is to update and streamline requirements and to remove regulatory obstacles that would impede the effective implementation of OBD-I/M testing.

Copies of the proposed rulemaking are available via the Internet at www.epa.gov/oms/epg/regs.htm.

A Brief History
Section 1968.1 of the California Code of Regulations (CCR) was originally adopted by the California Air Resources Board (CARB) on September 14, 1989. The CARB folks are the ones responsible for developing OBD II with the help of the Society of Automotive Engineers (SAE), and this section of the CCR is the regulation that requires manufacturers to implement on-board diagnostic systems on new motor vehicles.

I've been an emission inspector in Colorado since our first tailpipe testing way back in 1982. During the years since, I've seen the program evolve into our current centralized I/M 240 test. Now, in accordance with the Clean Air Act of 1990, our program, and all others in the U.S. and Canada, will need to incorporate an OBD II check as part of the pass/fail criteria. If you're an emissions repair technician, a shop owner or a service manager, you need to know the changes occurring in OBD technology and emission program legislation.

What Does I/M Look Like Today?
There are currently 35 states running enhanced or basic I/M programs. Some of these states have newer programs that are still having the "bugs" worked out and are trying to build momentum and consumer confidence. Other programs are mature and are looking at the next logical step: OBD II testing in their inspection lanes. Wisconsin, Utah, Colorado and Vermont have all been performing OBD II checks in their testing facilities in preparation for the proposed phase-in.

So what do these changes mean to you? In a word, opportunity! From the days when we could interpret our own HC and CO readings, write the sticker, lick and stick it, to the past five years of more complex enhanced I/M 240 failures, we've performed hundreds of emission inspections and repairs. These emission programs, and the training that we have all embraced in order to respond to them, have allowed us to increase our driveability troubleshooting skills and become better diagnosticians. Even if you're not repairing vehicles to pass an emission program, you will need to become proficient in the ways of OBD II, since 110 million vehicles, or approximately 50% of the vehicle fleet, will be OBD II equipped by 2005.

Why An OBD II Check?
On August 6, 1996, under the authority of the Clean Air Act (CAA) as amended in 1990, the EPA published rules requiring the use of On-Board Diagnostics (OBD) in inspection and maintenance (I/M) programs. This provision required I/M programs to incorporate an OBD check of OBD-equipped vehicles in addition to traditional tailpipe testing on January 1, 1998. The Agency decided to delay the mandatory startup of OBD I/M until January 1, 2001 for a variety of reasons. The primary reason was that there was little data on the performance of OBD systems in-use, given the relative newness of OBD technology. An additional concern existed over the level of understanding of the technology in the states and the repair industry. During the delay period the EPA conducted a test program to evaluate the usefulness of OBD for I/M and to determine the associated emission benefits.

The EPA's study provided preliminary answers to the following questions:

Is there a benefit of identifying the emissions problems of vehicles with the OBD system and how does it compare to the available tailpipe tests?
Will OBD pass any vehicles that are emitting at levels that are of concern in I/M?
A total of 201 vehicles qualified for this program, 194 with the Malfunction Indicator Lamp (MIL) illuminated and seven high emitters with no MIL illumination. After testing these vehicles the EPA concluded that:
OBD technology is a viable I/M test for 1996 and newer vehicles. The emission reductions available from basing repairs on OBD appear to be at least as large and possibly larger than emission reductions obtained from I/M tailpipe tests.
OBD did miss some high emitters but performed better than available I/M tailpipe tests.
Some areas of OBD technology still need to be refined and the vehicles with OBD technology should be monitored for the effect of aging.
OBD I/M offers preventative maintenance, which allows benefits previously unavailable to I/M programs to be claimed.
A Look at the Wisconsin Program
Wisconsin is currently conducting OBD-I/M checks in conjunction with a biennial, centralized, I/M 240-based enhanced I/M program, which also includes a separate gas cap pressure test. The OBD-I/M check is only conducted on MY 1996 and newer light-duty vehicles and light-duty trucks, and the results of the test have been purely advisory (i.e., vehicles are not being rejected or failed on the basis of the OBD-I/M check at this time).

The program data EPA analyzed included I/M 240, gas cap and OBD MIL illumination and readiness data for more than 116,000 1996 and newer vehicles The data was analyzed to determine the size of the readiness problem, the number of model years affected and the approximate percentage of vehicles that would be rejected under a variety of possible readiness criteria. EPA also looked at the frequency of MIL illumination across model years and vehicle types, and compared the relative failure rates of OBD-I/M to that of lane-based I/M 240s and gas cap tests. Lastly, EPA compared mileage accumulation and vehicle age data to MIL and readiness rates to determine the impact of vehicle age and mileage.

Since August 1998, Wisconsin's I/M program contractor, Envirotest Systems Corporation, has been sending the EPA staff OBD scanning and I/M 240 test results data collected on 1996 and newer vehicles coming through the Wisconsin I/M test lanes. The data provided by Envirotest includes vehicle identification, and I/M 240, OBD-I/M and gas cap test results. In analyzing the Wisconsin data, EPA focused on: 1. the readiness status of the OBD monitors; 2. the frequency of MIL illumination; and 3. the relative failure rate of OBD-equipped vehicles based upon OBD-I/M, I/M 240 and gas cap evaporative system testing.

The following observations were made:

The majority of vehicles showing up at the I/M lane with monitors reading "not ready" were from 1996; the "not ready" rate for 1996 vehicles was 5.8%.
Vehicle "not readiness" dropped off with each successive model year to 2.2% for 1997 and 1.4% for 1998.
After the first 40,000 miles, MIL illumination seems to increase with mileage and age. The greatest MIL illumination rate was seen among 1996 vehicles (2.5%) followed by 1997 (0.7%) and 1998 (0.5%).
The OBD-I/M and I/M 240 tests fail roughly the same overall number of 1996 and newer vehicles but very few vehicles fail both tests.
The stand-alone gas cap evaporative system leak test fails several times more vehicles than does the OBD-based evaporative system monitor.
OBD Readiness Indications (Monitors)
The readiness indications ensure that the vehicle has been driven sufficiently for the OBD II system to test all the emission control components and determine whether or not a fault is present. Secondly, readiness indications also combat fraud in I/M testing. It was possible with OBD I vehicles to erase fault codes just before a vehicle was subject to the I/M test, thus enabling a malfunctioning vehicle to falsely pass an I/M test. If fault codes are erased on an OBD II vehicle, the readiness indications are set to incomplete at the same time. If a fault remains, it will be detected again before all readiness indications are set to complete. Therefore, it is important for all readiness indications to be complete before subjecting a vehicle to an I/M test.

The OBD system monitors the status of up to 11 emission control-related subsystems by performing either continuous or periodic functional tests of specific components and vehicle conditions. The first three testing categories - misfire, fuel trim and comprehensive components - are continuous, while the remaining eight only run after a certain set of conditions has been met. The algorithms for running these eight periodic monitors are confidential to each manufacturer and involve such things as ambient temperature as well as driving times and conditions. Most vehicles will have at least five of the eight remaining monitors (catalyst, evaporative system, oxygen sensor, heated oxygen sensor and exhaust gas recirculation or EGR system) while the remaining three (air conditioning, secondary air and heated catalyst) are not necessarily applicable to all vehicles. When a vehicle is scanned at an OBD-I/M test site, these monitors can appear as either "ready" (meaning the test in question has been run), "not ready" (meaning the test has not yet been run) or "not applicable" (meaning the vehicle is not equipped with the components in question).

Current federal regulations for OBD-I/M testing require that I/M programs reject from further testing any 1996 or newer OBD-equipped vehicle that is found to have one or more unset readiness flags. The reason vehicles with unset readiness flags are rejected but not failed is because an unset readiness flag is not necessarily an indication of an emission problem. Rather, it is an indication that certain monitor(s) that are intended to determine whether or not there may be an emission problem have not been run to evaluate the system. In the case of rejection, the issue of whether or not the vehicle requires repairs is deferred until the readiness flag(s) have been set and the monitor(s) run.


To determine the extent to which vehicles may be appearing for their OBD-I/M check with unset readiness flags in the real world, EPA looked at OBD readiness data from Wisconsin's I/M program for the last five months of 1998 and the last eight months of 1999.

The majority of the "not ready" vehicles are 1996 LDVs (6.9%) and the majority (77%) of all "not ready" 1996 LDVs were not ready for the catalyst monitor, while 1998 LDVs were more frequently "not ready" for the evaporative system monitor. By 1998, the "not ready" rate for LDVs dropped over five-fold - from 6.9% to 1.3% - while the overall "not ready" rate for 1996 vehicles (5.8%) dropped more than four-fold. Mileage may play a part in these differences, since the '96 vehicles had three year's worth of accumulated mileage, while 1997 and 1998 both represent only a single year of mileage accumulation each. EPA has no data concerning how many of these vehicles may have had a MIL illumination in the past which resulted in a repair. The study also showed a decline in MIL illuminations until about 40,000 miles, followed by a noticeable increase in MIL illuminations. It should be noted that the warranty period for comprehensive coverage on these vehicles expires at 36,000 miles.

A Glimpse at the Utah Program
In Davis County, UT, 65,927 vehicles were tested between January 1, 1997, and July 31, 1999. Of these, 91.33% tested "good," 4.76% tested "not ready," 2.26% had standardized diagnostic trouble codes (DTCs), 0.74% had their MIL on and 1.48% were unable to communicate.

The Colorado Program
I asked Doug Decker, with the Colorado Department of Public Health & Environment, how effective he felt OBD II is as a tool for identifying emission failures. He cited a study by CDPHE which states, "The results of this study indicate that OBD II is a very effective strategy for identifying vehicles with either high emissions or potentially high emissions. However, the data generated from this study indicate that if OBD II MILs alone were used to predict FTP pass/fail, the false identification rate would be 60%, i.e., 21 of the 35 study vehicles that failed OBD II (MIL illuminated) passed the FTP!"

A second way of looking at OBD II is to determine if the stored DTCs actually identify an abnormality. For regular mileage vehicles, OBD II DTCs identified system or component problems that were in need of repair and/or that could have eventually resulted in high emissions 94% of the time (30 of 32 vehicles). For high mileage vehicles, the identification rate was 67% (six of nine vehicles). Using this criterion, OBD appears to be a reliable tool with which to identify high emitters or potentially high emitters. However, when OBD II DTCs indicated component or system problems, 18 of the 31 identified regular mileage vehicles and five of the seven identified high mileage vehicles passed the FTP. As a result, the DTC false identification rates with regard to federal in-use FTP standards were 58% and 71% for regular and high mileage vehicles, respectively.

Decker goes on to say, "this is one of your worst nightmares - a vehicle that failed OBD II for a lit MIL in the I/M station. This vehicle is now in your shop for repair, and its emissions levels are cleaner than when it was new; and approximately 10 times cleaner than the I/M standard. There is a problem with the car, but it may cost the motorist $400 or more for a negligible emissions reduction (and likely no change to driveability or fuel economy)."

There are a number of reasons why readiness indications may not be set at the time of inspection. If a vehicle with the MIL illuminated was repaired shortly before an I/M test and had fault codes cleared subsequent to the repair, the vehicle may not have been driven sufficiently to exercise all of the major monitors before being taken to the I/M station. In some cases, vehicle operation in extreme ambient conditions will prohibit the monitors from running and setting readiness indications.

Decker goes on to make a good point: "When a tech repairs an OBD II problem and clears codes, the readiness monitors need to be reset before the car can be retested. Who will do this? The motorist? The shagger? It may take a couple of days of "normal' driving to reset monitors. What about the procrastinator whose registration expired yesterday and is now driving around trying to reset monitors and gets a ticket? Will the motorist see the tech's unwillingness to reset monitors as poor service? Supposedly, some manufacturers have already established a key cycle test that flashes the MIL to indicate whether the monitors are set or not. Service advisors will need to have a script to work from, like a FAQ, when dealing with OBD II and MILs."

Is the Future of I/M Just OBD II?
No. Tailpipe testing will be around for many years to test all of the pre-OBD II vehicles. Also, as OBD II vehicles age, emission tests will be needed to ensure the accuracy of those on-board systems.

Clearly, there are many questions that have arisen from the comparison between current I/M programs and OBD II testing. Is OBD technology a viable I/M test for 1996 and newer vehicles? From my research, the answer is "Yes." Are the emission reductions available from basing repairs on OBD at least as large and possibly larger than emission reductions obtained from I/M tailpipe tests? Again, it is "Yes."

Some areas of OBD technology still need to be refined and the vehicles with OBD technology should be monitored for the effects of aging. Also, OBD I/M offers preventative maintenance, which allows benefits previously unavailable to I/M programs to be claimed. I predict that as a result of the move to OBD II testing, we will see fewer "bad" catalytic converters, because the on-board monitors will catch honeycomb-destroying misfires before they kill the catalyst.

I'd like to share a statement from CARB's website to conclude this article on OBD II: "One of the primary goals of the OBD II program is and always has been to improve the availability of service information to the aftermarket repair industry. As such, the OBD II regulation contains several requirements for standardization of diagnostic connectors, communication protocols, fault codes, engine parameter data and test equipment. Additionally, CARB has proposed new amendments improving the availability of diagnostic and repair information for all emission-related repairs. These requirements will allow independent repair shops to utilize a single diagnostic tool to access all of the information generated by the OBD II system for any manufacturer's vehicle. CARB believes these steps are clear indications of CARB's continuing commitment to the aftermarket service industry."

For more information on On-Board Diagnostics, visit underhoodservice.com and click on "Search Back Issues" to begin your search for OBD.

Tech Tip Corner
The O2 Sensor - Troubleshooting & Maintenance

You can test O2 sensor voltage output and response time with a propane torch and a digital volt-ohm meter, using 10 meg-ohm impedance in the volt meter circuit. To do this, hook the voltmeter to both wires of a two-wire sensor and to the single wire and to the shell of the O2 sensor on a single-wire type. Clamping the one wire sensor in vise-grips and hooking the voltmeter lead to the pliers saves the fingers.

Heat the O2 sensor with the torch and observe the voltmeter. You should see the voltage climb to 0.6V in 15 seconds, then on up to 0.8V in the next 45 seconds. Remove from flame and voltage should drop to less than 0.2V in less than four seconds. Repeat this test two more times in succession. If it meets the voltage and time specifications, then this indicates the O2 sensor is capable of communicating with the computer and giving fast and accurate air fuel ratio information.

The faster the O2 sensor responds, the faster the computer makes corrections.

Recommended intervals for O2 sensor testing are every 20,000 miles or every tune-up or any time you suspect a rich-running condition or the use of leaded fuel. Also, this test should be performed any time the computer stores code 13, 44 or 45 on a GM car, or any other vehicle where computer codes indicate O2 or rich or lean conditions.