Smog Check

I have a 1991 Honda Accord with about 270K miles. The car consumes about a quart of oil every 2k miles, seems to otherwise run fine. The car is due for a smog check. Would I be better off having the engine tuned before I have it smogged?

What state do you live in? What are the consequences of a failed test (besides being out the cash?) Does it run fine, otherwise?

I’d: change the oil, check the air filter (change if required), determine when the plugs were last changed–change if it’s been >60K mi. (Is it a 4 or 6 cyl? Plugs are much cheaper/easier to change on 4 cyl cars!)

If there’s no prejudice associated with a failed test, that’s about all I’d do (assuming running good); I’d take the test and (if failed) use it as a diagnostic for what to fix next. Note that many states exempt vehicles over a certain age; 25 years is a big threshold, so this might be your last test! (Or, you could live in California.)

You might want to try these smog tips, especially the one about running the car at highway speeds for 2 weeks prior to clean out the catalytic converter. That will be especially important since your engine is burning oil. You might also want to try the Blue Sky additive.

I’m very thankful that I’ve lived in states that did not require a smog check/safety check for my vehicles. I have no doubt that they would pass said inspection but I see it as unnecessary for the most part. I may be wrong but that’s how I feel and I’m glad those states felt the same way.

There are 33 states that don’t require annual smog checks or safety checks.

Smog checks wouldn’t bother me if the requirements were realistic. Many states have committed (to the EPA) to OBDII checks instead of tailpipe tests, on the basis that the EVAP system is a crucial part of emissions reduction (EVAP is, in truth, a system to prevent evaporative emissions), but the requirements have become ridiculous. The level of PPM required is almost zero, and the systems have become prone to false positives, and have become complex and difficult to diagnose as a result.

When you go for the test, take a 20 to 30 minute drive on the highway at highway speeds, then get the test. Maryland recommends that to help you pass the first time.

Besides making sure via a visual check that all the smog equipment that was there originally still is, I’d show up at the test site with a thoroughly warmed up engine, new air filter, new spark plugs, and recently changed oil.

Yeah Minnesota is one of those that did away with it some years ago. Concluded the only benefit was for the vendors performing the tests. Like I said a recent study concluded 2000 people a year in the metro area dying on the streets from bad air. That’s five a day. Funny but in 40 years I never saw one dead one from bad air. Of course they concluded that their are more deaths in the poor and minority neighborhoods. I don’t know how that works. As one who lived miles from the stockyards, it seemed that the bad air seemed to cover the entire area without discriminating. I suspect some objectivity may have been left at home.

In my experience, there are quite a few vehicles out there that will pass an OBD2 “smog test” . . . but will still fail the tailpipe test

I’ve worked on quite a few, actually

So don’t anybody be smug and suggest that OBD2 catches everything, and can prevent pollution. In fact, there are dirty cars out there that won’t set any codes and won’t turn on any light, ever

But I do realize that the plug-in tests are more efficient, from a financial standpoint

And we also have to accept that the plug-in test is not perfect. It’s a pretty decent compromise, though

I remember back in the days of CIS that checking the tailpipe emissions were part of the PDI on new SAABs. That meant checking HCs and CO with an infrared machine.

The spec has long been forgotten but we had to tweak all of them. I seem to remember them coming in at .75% or something like that on the CO and every single one of them had a slightly rough idle.

That presented a problem as a test driver or new car buyer is not going to be happy with a rough idle; especially with an automatic transmission.
So that presented 2 options; one is leave them be with the rough idle and kill sales or tweak the CO to 1.25% where they would idle smooth and which was illegal as hxxx.

It’s not difficult to figure which option was used…

If it ever became an issue we pretty much had the boilerplate answer down, " Well, it was fine during the PDI. It’s CIS; who knows…".

One question I’ ve always wondered about for Calif smog check is what advantage treadmill testing provides over simple idle testing? Many cars here – my Corolla included – are required by the Calif Emissions rules to be put on a treadmill and tested at 15 and 25 mph. They measure the tailpipe emissions at each speed and decide from that if you pass or not.

It seems to me that what they did before switching to this technique – a tailpipe test at idle – would accomplish pretty much the same thing. I just can’t image gaining much from testing on the treadmill.

Why do you think they do that? B/c it is possible for the car-owner to hack an idle test more easily than a treadmill test? i.e. the car owner could rig things up so it would idle and pass emissions ok, but it wouldn’t then run ok at any speed above idle?

Even if that were the case, how many people would go to the trouble to figure that out? I mean, really! Or am I missing something?

^I think NOx is better measured under load, when the engine is running hotter. At least I recall reading that somewhere.

OBD II tests were implemented to help try and prevent emissions testing fraud, which was rampant with tailpipe testing. It is MUCH harder to fake out a computer plugged into an OBD II port. Back in the days of tail pipe testing I was able to get a problem car “passed” at my favorite mechanic’s shop. That “option” is no longer available in my state.

It’s easy to tweak idle emissions.
A “friend” (wink, wink) had an '81 Accord with a number of aftermarket parts (non CVCC head, cam, Weber carb, exhaust headers) and a hollowed out cat converter.
Raise the idle speed a bit, retard the timing a little and set the idle mixture a bit lean and it passed the idle test.

I wholeheartedly agree with db that a vehicle can the OBDII download while still producing emissions in excess of the requirements.
However it’s also true that a vehicle can pass a tailpipe test while the gas tank is leaking.

I think the OBDII download tests were accepted by the EPA because they theoretically check the systems that can produce evaporative emissions while still checking for operating problems that can produce tailpipe emissions… at least in theory.

Honestly, I believe that by mandating the emissions requirements that the manufacturers are held to, and recognizing that most operating problems will either cause the owner operating problems, the amount of emission reduction accomplished by annual emissions testing is inconsequential. In the early days of the Clean Air Act, and to the requirements of t he early days, tailpipe testing was probably necessary, but now I think it’s more politics than emissions-reducing. I know that philosophy will be controversial, but I think we’re past the point of diminishing returns with the emissions testing system.

I realize too that the feds are now looking at CO2 reduction, as the Europeans have been doing for some time now. CO2 being the natural byproduct of full combustion, the gas we breath out, and the gas plant life breaths in, I have serious reservations about that one, but it’s about to be regulated anyway. More pandering to another special interest group.

Well, in my home state of PA, they do emissions and safety. By law, the emissions has to be done first, which I think is asinine. I mean, if you flunk emissions (and drive it around while you hunt parts to fix it), wouldn’t it be nice to know if your ball joint was getting ready to separate? (Or similar?)

I recently had to smog a 2010 car in CA and all the shop did was hock up the OBDII to the computer and since there were no codes, I passed. No tailpipe/etc like my other cars (2000 & 2005). I asked the shop owner since I go there frequently to make sure that is all there is to it and the owner said; yes.

As much as I like the shop, felt somehow taken to pay $40 to know that my CEL is not on.


It’s a little more complicated than that

You were most likely directed to a “star” station

Old cars don’t get sent to those inspection stations

My car is 2005, and that’s where I went

It’s not so simple as no light, and you pass

If the check engine light is on, you fail

If there is a code which is commanding the light on . . . whether it is on, or not . . . you fail

The presence of codes does not automatically constitute failure. For example, a knock sensor code will generally not command the mil on

If you don’t have the required number of complete readiness monitors, you fail

If you have an evap problem, for example, and you don’t want to fix it, and you’re due for a smog . . . you’ll have to figure out a way for all the other monitors to successfully run to completion, yet create a condition in which the evap monitor does NOT run before you show up at the inspection station.

Usually, the question is how to get a monitor to run to completion.

However, in this case, the question is how to create a situation, so that a monitor won’t run to completion, at least not at the moment

I won’t be posting the answer to that question, but it’s pretty obvious for professional wrenchers reading this

There will always be some way to “game the system” if you’re resourceful


By the way, depending on which monitor is incomplete, a savvy smog guy could deduce what kind of problem you may be hiding. But if the car is ready to be “tested” . . . whether it’s merely a plug-in test, or the works, including dyno, then he’s not really supposed to judge you or say he’s on to your game

After all, maybe that lone monitor is incomplete, because a battery was recently replaced

Thanks for the detailed info. My 2005 Camry still gets the tail pipe test even without CEL or codes. This is a test only station, not really required by my notice, but I still like the test only stations since I feel there is no conflict of interest (as trying to sell me repairs I might not need) and this shop is also easy to get in & out and the guy is nice, so I feel good about giving him my business.

I still think for newer cars, if there are no codes, spending a minimum of $40 to get a certificate is too much.


What do feel would be an appropriate fee?

The guy plugging in has to make a fair profit, in my opinion

He’s not pocketing that $40, and he’s probably only getting a small part of it for himself. When you subtract any overhead, it was probably hardly worth his while to inspect a vehicle

Especially if it’s one of those shops that is not even set up to do any repairs