Clearing a code causes the computer to go through the self diagnosis and 'learning' mode. There is a specific set of parameters the engine must go through to establish 'ready' mode, and, depending on your driving habits and length of trips can take quite a while.

The mechanic shouldn't have cleared the code and should have told you that the check engine light(CEL) will turn off once a few drive cycles have been completed. But no one wants a car back from a repair shop with the CEL on, so it is cleared and the not ready status takes much longer to go away.

Disconnecting the battery just made matters worse!!! Now, all of the electrical/mechanical systems have to go through the 'learning' process all over again, so it could be a month of Sundays before you get a ready status and are able to get 'tested'.

Klaus
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Always willing to listen, just not able to take direction.