Help me reset my car's computer in time for Saturday's emissions test
January 29, 2015 5:01 AM   Subscribe

Of course my check-engine light comes on 4 days before the deadline to get my emissions tested. The issue got fixed yesterday, but they told me it could take up to a week to reset my car's computer--and if I got my emissions tested before it fully reset, I'd fail. Can I put my car through all the necessary paces in 3 days?

They told me the three big things I had to do was stop-and-go city driving (check), sit overnight with half a tank of gas (check), and drive on the interstate (check). What else does my car need to do to pass the emissions test by Saturday?
posted by elizeh to Travel & Transportation (11 answers total) 2 users marked this as a favorite
I don't think that's how this works. I've literally gotten an emissions issue fixed, had the check-engine light go off, and driven directly to a testing station, where I was tested and passed just fine. Is your light still on? If it's not, my experience in two different states is that you can head over right now and it'll be fine.
posted by MeghanC at 5:13 AM on January 29, 2015 [1 favorite]

Go to your local Advance/AutoZone/O'Reilly's/etc, tell them your check engine light is on but the problem's been fixed and you need the light cleared. They should do it for free.
posted by TomMelee at 5:18 AM on January 29, 2015 [2 favorites]

Google 'drive cycle after reset'. What you need to do may vary based on the make and model of your car - when this happened to me, my mechanic was able to print out a sheet for me with the specific drive cycle for my car. Maybe your mechanic or a dealer could do the same for you.
posted by southern_sky at 5:19 AM on January 29, 2015 [2 favorites]

the check engine light isn't what says if the emissions are good to go, theres another emissions system indicator that gets read. After driving around for a while you should be able to have autozone or your mechanic check for you with their scan tool if the emissions system is good to go. (my OBD2 scanner has red/yellow/green lights for emissions, separate from the normal code reading functionality).

I'd drive for a continuous hour on the highway at speed and at least 30 mins continuous in stop and go, but thats just guessing.
posted by TheAdamist at 6:01 AM on January 29, 2015

Best answer: Yeah, drive cycles. You may need to put a hose on the the coolant temperature sender to get it to think it's starting from really, truly cold. My drive cycle:
Start from absolutely cold engine.
Start vehicle, put it in drive, turn on a/c and defroster. Sit there for 150 seconds at least. Turn off a/c and defrost.
Drive normal-to-gently to the nearest interstate. Make sure you have a couple stop signs, lights, etc. on the way.
Accelerate to 57 mph with half throttle, set the cruise, and go for five minutes. Keep it between 55 and 60.
Coast as much as possible to the next exit, turn around, and head back, accelerating using 3/4 throttle to 57.
Coast as much as possible to your original exit, drive home.
Shut the car off, let it cool down completely, repeat.
Note that you must have between 1/4 and 3/4 tank of gas.

I believe AZ or O'Reilly can check to see if everything's reset. The key word you're looking for is Readiness Monitors.
posted by notsnot at 6:07 AM on January 29, 2015 [1 favorite]

Depending on the year, you may be able to get an inspection with one or two readiness monitors not set. Ask your mechanic.
posted by notsnot at 6:08 AM on January 29, 2015 [1 favorite]

Best answer: Does your state have state test centers or independent garages conduct the test? My state offers residents a choice, either the state test centers or the contracted independent quicky oil change garages. At the state test centers, residents can choose from the quick, plug under the dash test or a dynamometer test. The dynamometer test has big rollers that the car sits on, they put a probe in the car's tailpipe, and a guy "drives" the car while on the rollers for a minute or two. The dynamometer test is for cars like your that don't have a drive history yet because of a recent repair. This dynamometer test is the one you need to request.
posted by dlwr300 at 6:13 AM on January 29, 2015 [2 favorites]

Be very careful about this - you're likely to fail your inspection, and the inspector won't be able to get a reading as to why (necessary to tell you what you have to do to pass it upon re-inspection). Speaking from experience here...
posted by NotMyselfRightNow at 8:51 AM on January 29, 2015

Response by poster: Drive cycle, thank you! I got my advice to drive for "up to a week" to reset my computer from two different mechanics, so I would assume completing the drive cycle is necessary for the test in my state.

I will also tell the testing center I had a recent repair and ask them to use the dynamometer anyway, because surely they still use one for older cars, right?
posted by elizeh at 9:21 AM on January 29, 2015

Assuming you still have the card/letter telling you to go get the test done, read it. The engine light in my car did the same thing last time, and the garage told me the same thing.

The card explicitly said the light being on would not be an instant failure, presumably because garages keep feeding people this line. (This obviously might be different wherever you live.)
posted by Su at 11:13 AM on January 29, 2015

the check engine light isn't what says if the emissions are good to go

elizeh didn't say what state they're in. in my state, if the light is lit for any reason they wont even hook up the machine and test you. it's just too bad, go home.

the autozone/o'reillys recommendation is spot on. i've done exactly that before. just have them bring out their scanner and clear the code. if what caused the code is resolved, it won't come up again.

Ask the person at the counter though, and they should know: in some states you can't have cleared the codes within X amount of time or they'll tell you to come back later.

The drive cycle thing could/should also clear it, but there has to be some way to just reset it with a scanner. If there's either the state rules on resetting, or that isn't possible on this car though then... ugh.
posted by emptythought at 2:47 PM on January 29, 2015

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