My mom has a ford taurus and she failed emissions test a while back and were not just getting to it.

So she had a check engine light on for about a year(lol) and we got it fixed so now the check engine light is off finally. The mechanic said he reset the engine light and to drive the car for 2 days and it should be erased from the computer, thats what the mechanic said but the only problem is my mom tags are dead after 12 tonight.

She needs to redo the emission test but do I have to wait until 2days to drive it becaise the check engine light is off,or will the emission computer still detect the problem through the car computer. Athought her light is off I remember somebody on her saying if you disconnect the battery for 30 minutes that it will erase the code, is this true.

Any help would be appreciated.