Building emissions history to pass smog test

Many newer computers will read sensor data constantly, but in the case of a smog test many sensor data needs to be continuously reading for two or more hours of engine running time to collect enough saved "history" for smog testing.

It prevents persons from willingly deleting data (by unplugging sensors or battery disconnection immediately prior to testing to pass smog.

This is common in the Nissan's could be the cam and crank sensor these go at around 70000 to 120000 should do both at once to be safe. that will fail an emissions test for sure. hope this helps

Disconnecting the battery resets the PCM - engine computer ,an the emission monitors . A drive cycle has to be done to get the monitors to run an hopefully set. That's all you need to do is drive it for few days of different driving conditions - city , highway ,from cold start . google GM drive cycle . OBD Monitor Not Ready

Your vehicle is equipped with an OBD II computer AND a link to connect OBD II computer to a Smog Check Analyzer or Data Scan Tool (available
at most auto part stores).There are two types of codes, bad codes and good codes. The good codes are the "Readiness Flags". These Readiness Flags
indicate that certain emissions systems which the OBD II computer has been monitoring have PASSED the test, indicating that those systems are
working properly. Then there are the bad codes. The bad codes are actual "Trouble Code". These codes indicate that the OBD II computer
has detected a problem with in the emissions system. The Trouble Code will specifically indicate the component and problem which was found.
Newer vehicle's have very complex codes in the thousands.
"Readiness Flags" do not cause the "Check Engine" light to illuminate, but may cause a vehicle to fail the smog test.
In order to set all the proper "Readiness Flags" the OBDII system must complete at least one drive cycle (in some cases
two or three). A drive cycle is a sequence of internal tests which the OBDII computer runs while your vehicle is being driven. This insures
all emissions systems are functioning properly. Only then will your vehicle pass the smog inspection. A drive cycle usually requires one
week of driving.

change your oil and oil filter. Add a bottle of octane boost to the fuel tank then top off with fuel. Drive vehicle for about twenty minutes then have emissions tested. Unless you have a bad catalytic converter, you should pass emissions.

Just because the car seems to run well, does not mean the emissions are within spec. For example, you could be running a little rich and the car will start and run great, but the exhaust is not within code.
What you can do is take it to a "smog shop", that is a repair shop with the proper equipment to diagnose the problem. If the testing is simply the reading of the on board computer codes, then most any place can read those, but you need an experinced mech to know what to do about it. May need an exhaust gas analyzer to physically sample and analyse the gasses. For the actual test, as long as the computer says all is fine, usually, you're good to go.
If the computer looses power any saved run data will be lost and must be re-accumulated to pass the smog test. A few hours to a day is usually enough run time to accumulate enough data.

Take it to autozone or another place like it and have them read the codes and tell us what they are.

Check the help link
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Vehicle smog test failed Due to NO MIL/check engine light?
http://schematicsdiagram.blogspot.com/2011/12/vehicle-smog-test-failed-due-to-no.html

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To review - - after you disconnect the battery you need to drive the vehicle at highway speed for 20 - 50 miles to allow the computer to "re-learn" the data parameters. This means getting the engine up to operating temp and speeds of at least 50 mph.
If the engine does not reach operating temp some of the sensors will not be active yet.