# Won't pass smog because of computer, any suggestions?



## raider32assasin (May 5, 2005)

My 1996 Sentra will not pass smog because of the computer from what my smog guy says. he says that because I lost power at one point (left my lights on all night, so had to recharge the dead battery) so now it will not pass one of the tests. He tells me I need to fill my tank up and drive on the freeway for 200 miles to get the computer back to the way it should be. Is this right? Any suggestions on what I should do? Any help would be much appreciatted. Thank you very much. Also, it passed evreything else with no problemat all.


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## Madmaxfl (Oct 22, 2005)

raider32assasin said:


> My 1996 Sentra will not pass smog because of the computer from what my smog guy says. he says that because I lost power at one point (left my lights on all night, so had to recharge the dead battery) so now it will not pass one of the tests. He tells me I need to fill my tank up and drive on the freeway for 200 miles to get the computer back to the way it should be. Is this right? Any suggestions on what I should do? Any help would be much appreciatted. Thank you very much. Also, it passed evreything else with no problemat all.


I do not know specifically aboiut this car but some cars will go into a default setting when the battery goes dead and there is no power to the ECU. Typically the ECU will relearn the correct settings and modify the settings for the most efficient running of the engine. I do not think it normally takes 200 miles but maybe a trip out on the freeway for 10 miles or so combined with some stop and go driving. what do you have to loose. Did you run the codes to see if there was anything else causing high emissions?


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## nova73guy (Mar 30, 2004)

Sounds right. When the computer "dies" it goes back to default mode. There are several readiness tests that must be run before the smog computer will pass it. Included are the evap leak test, O2 sensor readiness test, O2 heater test, etc. He should have given you a print-out of which tests didn't pass. There are a couple that take a while to run, so driving 200 miles (a little high in my opinion) should give plenty of time for the tests to run and pass. Unfortunately if you don't have a scan tool, the only way to tell if they passed would be either get the smog check again or pay a shop to check them for you.

Just be glad they aren't sticking the sniffer up the tailpipe. Failing that test is even more of a headache.


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## Recian (Sep 30, 2008)

it's because the emissions computer in a smog test hooks to your ECM and reads what' sknown as "Readiness monitors" your car has to go through a certain drive cycle for O2, Catalyst, Evaporative etc etc diff readiness monitors. and each has it's own different conditions that have to be met in order to complete the cycle. usually O2 or Evap are the hardest to complete but some states you can pass with 1 not ready or (older cars 96-97 in NC) you can pass with 2. most cars have 5-7 monitors im thinking the B14 only has like 4. 

Nissans arent picky about fuel level. just drive it for a few days to a week. mileage isnt important just try to do differnt types of driving like freeway, city, country etc diff drive cycles and they'll reset. Dont worry this is normal when your battery dies it's a temporary memory stored in the ECM


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## Jr71vette (Dec 13, 2003)

the " readiness " tests on any vehicle usually occur while the car is warming up from a cold start-once the car has fully warmed up, and the car is at operating temperature, the readiness tests have been performed. it is basically the computer checking all systems and making sure all sensor readings are at normal parameters. The battery dying excuse sounds like bull, but the car would be in re-learn mode, which still makes no sense. did you have a check engine light on, or codes stored in the computer? that would cause you not to pass a readiness test?


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## Recian (Sep 30, 2008)

you dont have to take my word for it on the battery. im just a smog test inspector for the state of North Carolina. Any time an electronic device loses battery power it will default to it's factory setting which means (for most 2.5L Nissan 4cyls) idle air volume relearn has to be done, readiness has to be reset by driving according to drive cycles set by the manufacturer and short term fuel trims have to be relearned which isnt something u have to worry about


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