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We’ve touted code readers before. If you own an OBD-II-equipped (read: post-1996) vehicle, these little black boxes serve as the skeleton key to the check engine light (CEL) cellar door. But this weekend I was patching my F150 back together after getting it stuck in a friend’s lake of a back yard, and I discovered another great reason to own a code reader: the pre-emissions check.

In Texas, we have to get our vehicles inspected each year, and part of the inspection involves plugging the vehicle into an over-sized code reader — which checks to see if the car’s computer has detected any failures related to emissions. Since my truck’s due for inspection, I was concerned about the CEL. And rightfully so: When I jacked in the reader, I discovered the CEL was caused by — wait for it — an evaporative emissions failure.

Now since this light came on right after I left the truck running while up to its frame in mud for a bit, I suspect this might be a temporary situation. So I erased the code and reset the CEL. But if you end up doing what I’m doing, you need to know that the emissions test (at least in Texas) won’t pass you unless the car’s OBD-II has had time to complete a full cycle of the emissions tests. This will set a “has run” flag in the computer.

So if you’re planning to get your vehicle inspected after you erase the OBD-II’s memory (even if it wasn’t an emissions code you erased), you’ll have to drive the vehicle a bit before you can take it in for the test.

If you’re lucky (like me), your reader will have a handy red-yellow-green light system to tell you whether or not you’re ready for emissions testing. But if not, just remember to check for the “has run” flag — and absence of any emissions-related codes — before you go in.

Of course, if you don’t have a reader, you’ll have to just take off work, take your car in, and hope they don’t take your $40, walk back out 30 minutes later, and tell you that you’ll have to do the same thing again tomorrow or the next day because the computer’s not ready. Or worse yet, they tell you that you failed because of a random CEL. Doh!


16 Responses to Another Reason To Own An OBD-II Code Reader

  1. TXan says:

    Just had my 1988 Volvo turbo checked in Dallas County. They tried to throw the test by running the AC and turning off the overdrive (a button on the shifter). After the first fail, they were quick to recommend their $120 “injection system cleaning service”. Basically a bottle of Techron in the tank. Then I caught the light on the dashboard indicating OD lockout. And the AC compressor cycling. Scum.

  2. george says:

    readers are just that, readers. you need to get one that can read and also reset codes.

  3. danepants says:

    The Snapon Modus that I have access to has saved me quite a bit of money on car repairs for sure!

  4. shopmonger says:

    30 miles on a car will normally reset the NEED RUN setting on the OBDII although some need start and stop cyces to reset… some of the Chryslers needed 15 start and stop cycles.


  5. Discobubba says:

    @TXan: We have a similar system in Connecticut except I’ve luckily never had a problem with any of the testing stations.

    What I have had a problem with is the idiot bureaucracy of the system, their rules, and their ineptitude at correcting issues with their system/setup which is tied into the DMV’s too! On my daily driver they have continually not fixed my “re-test” date, which was never a problem as I’d just ignore it and go at the correct date. Except now the DMV started charging a $20 late fee! That’s as much as the cost of the test itself!

    I wouldn’t mind having one of these to help diagnose any issues, but luckily haven’t had to deal with emissions problems on my car (Tho I’ve had my share of other problems that’s forced me to use quite a variety of other tools).

  6. ZAW says:

    I just unplug the battery until stupid codes reset, drive around a for for a 30 miles. Drive into inspection station and always pass.

    Stupid EVAP sensor on jeep is defected and it cost way too much $$$ to replace.

  7. Chuck Cage says:

    @george, my reader (the one pictured in the post) does include freeze-frame viewing and code erase features.

    @ZAW, it can take a long time for a battery unplug to reset OBD-II, and some will never reset because of a battery disconnect.

    @TXan, I’m in the DFW area, too, and your experience is really crappy. Sorry to hear about it! I haven’t run into that before, but I’ve definitely run into people who make BS excuses to not test my OBD-I Miata or Porsche because they’re too lazy to put it on the dyno.

  8. Chris W says:

    Does anyone make a scan tool which doesn’t cost an arm and a leg? I have a $40 HF code reader which works fine, but I need to read a Chevy-specific sensor (CMP-CKP retard). It seems that scan tools cost much more than paying a shop to do the adjustment.

  9. Vic says:

    I’m not a hardcore environmentalist, but what about fixing the problem instead of resetting the codes to pass the inspection? Your truck and the atmosphere will thank you.

  10. Chuck Cage says:

    @Vic I didn’t just reset the code to pass the inspection. I checked out the associated hardware, found no issues, then reset the code to see if it returned after the test runs. If it doesn’t, then it’s as I suspected: My bit of off-roading caused a glitch. If it does return, I’ll located and replace the affected hardware.

    I wrote this up because even after you correct the associated issue you’ve got to reset the code and assure it doesn’t return in order to pass inspection.

    It’s all part of the process. 🙂

  11. Fabian says:

    The Actron CP9135 is a pretty high end unit which will sometimes hit $60 on amazon..


  12. BC says:

    AutoZone will scan codes for free, and Chryslers still have the old key flick method of pulling codes. Personally, if I were to buy a code reader, I’d just drop the coin and get something like the ScanGauge II, that way it’d be useful for something else as well.

  13. ChromeWontGetYouHome says:

    I second the ScanGauge II though from BC. It’s not the cheapest thing in the world, but if you consider it has a dual function to show you four real time sensors’ data including horsepower and torque, engine load, temperature, rpm, throttle position, etc. And you get freeze frame data with it.

    I’ve grown so accustomed to using it as a speedometer (my wheel generally blocks the needle view) it feels awkward to drive without it.

    In the lasy year, I’ve probably used it on about a half dozen coworkers’ vehicles and got a few of them out of inspection jams.

  14. russ says:

    @ Chuck Cage

    I agree with your use of the OBD-II reader. I do the same. Reset it first to check to see if it is a fluke.

    Where I live in NC anyone who has OBD-I gets the regular physical inspection only and pays $10 where as the OBD-II cars pay $30 and have their OBD-II checked. I wonder if the inspection stations complained about the cost to check both OBD-I and II? That I do not know. That is because they went away from the “banana in the tailpipe” test a few years ago. They found out that idling and checking the exhausts does no good. An inspector told me you would have to run the car for two hours with the sensor in the tailpipe to get an accurrate reading which is not possible. I do not know if this is true but that is what I was told by a few inspectors.

    Now for you California people I have heard of the smog inspection horrors not to mention the car ones also.

    I read an article, slightly over a year ago, which I wish I would have kept/boomarked, discussing about KS (I believe) and SC which stopped the state inspections and found no increase in car accidents due to poor safety issues years after they stopped. I found this hard to believe because I know of people that don’t even check the wear on their tires until it goes flat. NC was looking into this ( or acting like they were) but the politicians wanted the revenue — sorry for the opinionated view but politicians love taxes no matter how you disguise it.

  15. Jeff says:

    I bought a reader last year and it has paid for itself many times over by helping me diagnose problems with the wife’s Saab.

  16. ClydeCrashcup says:

    Ah yes, The California rules… Well, waiting in line at the smog insp. station, a dude ahead of me in a brand new Lexus failed. California has apparently given Lexus a pass for the first 3 or 4 years. Then you & Toyota have to belly-up to the repair counter. That was a couple of years ago. Smog laws here are vicious! I now only live 5 mins from work, and CA doesn’t make anything prior to ’74 pass smog muster, so I converted to a ’53 Ford F-100 with a 428 CJ. I can either spend it on smog issues, or rotten MPG in a vehicle I actually look forward to driving every day. 🙂

    That said (gleefully), My other vehicles all need to pass. Our ’97 Volvo is starting to have issues infrequently. My neighbor loaned me his INNOVA 3130c reader. Brilliant device has saved me mega-bucks chasing down everything from the MAF to several carefully hidden rubber vacuum elbows. An expensive unit that has saved many times its cost (Volvo dealers want your 1st born child). Surprisingly easy to fix most of these things with hand tools and some uninterrupted time for the pursuit.

    That said, After some superficial initial research, I intend to try the i-phone readers + APPs.

    Any thoughts on this?

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