My OBD monitor showed all as OK. My manual says that this means "monitor has completed diagnostic testing." During the emissions inspection, will the mechanic just plug a similar device into my car and check for the same OK readings, Or will he do a more invasive/thorough inspection of the emissions?

I am in North Carolina if that helps. I guess I'm trying to say does OK on my OBD monitor mean my car will DEFINITELY pass the test?


TL DR: Should you pass? Yes. Will you pass? There's no guarantee.

For the most part, yes. It will pass that part of the inspection. There is in some states, however, a visual inspection. They will be looking to ensure the EGR, cat converter, etc, are in place while doing the inspection. They do this because the triggers within the computer which relates to these parts can be "tuned out" by an industrious person. That means, these pieces might be missing, but because the parameters of the OBDII system which notes for this are changed so that it doesn't "see" the issue. If you have everything in place as well as having the drive cycle completed, your chances of passing the emissions inspection are greatly increased.

As far as how the inspectors do their thing, yes, it is my understanding they attach a computer which reads the same parameters as what your handheld device does. As long as your vehicle has done it's self diagnostics and completed the drive cycle, you should pass. You never know what funky things your local emissions might do, though, so that's the reason I say "there's no guarantee".

One thing to note: If you "clear the codes" in your computer, whether or not ther are any codes, you have to do the drive cycle again to ensure the readiness of the system. If you do that, you will not pass emissions testing until after you've completed the drive cycle.

  • I did clear the codes a few weeks ago for a check engine light. It hasn't come back up, and the only test that is "incomplete" is Evap monitor. So technically the drive cycle is not fully completed yet. But I heard that you are allowed to have One as incomplete per the EPA. There is nothing about this on the NC webpage though. Do you think I'm still fine if I only have Evap as incomplete? – Tom Mar 31 '19 at 23:21
  • @Tom - No. I'd suspect if you have one which is not cleared yet, it won't pass inspection. Not sure how SC does it, but in VA it wouldn't pass. It is still considered "Incomplete". – Pᴀᴜʟsᴛᴇʀ2 Mar 31 '19 at 23:25
  • Interesting to compare all this with the UK method: nobody cares what your software or your car sensors say - just stick a probe up the tail pipe and measure CO, unburned HC, and lambda at two different RPMs... – alephzero Apr 1 '19 at 0:33
  • @alephzero - That's what OBDII is all about ... emissions readiness. If you have OBDI, then up the tailpipe the probe goes. – Pᴀᴜʟsᴛᴇʀ2 Apr 1 '19 at 0:35
  • @Pᴀᴜʟsᴛᴇʀ2 in ny at least, you can pass the obd2 computer check with 1 monitor not ready on 2001 and up. Pre 2000 it’s 2 not ready. All we do in the non metropolitan area for emissions is visual check for emissions devices and plug it into a computer that checks monitors and transmits the pass or fail to the dmv. In ny city you’re put on a dyno and they do a exhaust gas analysis as well. – Ben Apr 1 '19 at 21:05

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