To OBD II Or Not

The downside is that, in order to accomplish all of these capabilities, more sub-systems, components (or their improvements), and monitoring software have been added, such as the fuel evaporative leak-detection system and its monitor. Failure sensitivity for other system monitoring, such as for catalytic converters and oxygen sensors, has been increased as well.

OBD II Obstacles
In real world terms, for example, this means that a Check Engine MIL (Malfunction Indicator Lamp) might illuminate if the fuel filler cap is not completely tightened, or the catalytic converters are operating much below 95 percent efficiency. In both cases, a trip to a qualified repair shop will be needed for diagnosis and, in the case of the former, resetting the check monitors. The latter would likely require replacement of the catalytic converter(s), a prospect considerably more expensive than on pre-OBD II vehicles.


If the state or area you live in has an I/M (emission Inspection/Maintenance or smog) test, an illuminated Check Engine MIL will result in a failure of the test. The difference with OBD II vehicles is that just resetting the self-test monitors to turn off the lamp will not allow your vehicle to pass the test, even if the measured tailpipe emissions are within prescribed limits.


The reason is that part of the I/M test on OBD II vehicles involves the test technician connecting his test machine's data link with the serial data port on the vehicle. If the self-test monitors have just been reset (generally within the past 50 miles), they will show a "not-ready" status, which will prevent the technician from certifying the vehicle. Rules are rules. So the vehicle will have to be driven long enough under a variety of driving conditions in order to "arm" the self-test monitors. If the problem that originally caused the MIL to illuminate is still present, the lamp will once again illuminate.

OBD I Pros
In contrast, pre-OBD II vehicles are not tested in such a stringent fashion. If the MIL is functional, but not illuminated during the test, and the vehicle passes the visual, functional, and tailpipe portions of the test, it qualifies for certification—even if there is a pending problem. When you consider that many catalytic converter replacements can cost well over $1,000, you can start to see the wisdom in owning a pre-OBD II vehicle.


Because of the OBD II issue, as well as the other considerations we discussed, purchasing an older vehicle may make sense for many people. This is not to say, however, that just any older vehicle will automatically be a better choice. Obviously, certain models, while perhaps evoking nostalgic feelings in us, no longer qualify as practical for daily use, or are not economically justifiable at this point in time.


It isn't difficult, though, to spot the vehicles that are. Generally, if the manufacturer and model have a good reputation, and there is an abundance of this model to choose from, that's a good sign. Survival of the fittest definitely applies here. Of course, it won't guarantee that all existing examples of the vehicle are worthy. As with any used vehicle purchase, employ due diligence by weeding out the bad ones by a process of thorough inspection. Purchasing an older used vehicle might not be "nobler in the sight of all men," but it can pay big dividends in the long run.