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2005 Elantra repeatedly failing smog test due to check engine light being on.

I purchased this vehicle a few months back and have tried repeatedly to get it smogged. Three stations later and still no pass or answer as to what is wrong. I keep getting told that the emissions are fine but there is something wrong with the computer. Two techs have told me to disconnect the battery, drive, and then come back. I have done this and the light went off for a few weeks but when I took it back it still didn't pass. If the emissions are passing then why is my car failing due to a computer issue with the check engine light? Is there something else that can be done? I am getting really tired of paying for tests and extensions with the DMV. Thanks!
Answer:

Your Hyundia Elantra's OBD II Diagnostic system is designed to monitor the engine emission conditions and report this information to the computer. This information is processed and checked against the computers pre-determined values for various inputs levels and performance patterns. If a decision has been made to alert the driver of an emissions problem, the "Check Engine" or "Engine Malfunction" light will illuminate on the vehicle's dashboard. The OBD II link relays all "Check Engine" conditions along with stored Trouble Codes with in the center database, to the smog machine during the time of the smog inspection. If any codes are present which cause the Check Engine light to illuminate either regularly or intermittently, the vehicle fails the smog inspection. 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. A vehicle will fail the smog inspection if the proper "Readiness Flags" are not set. A vehicle will also fail the smog inspection if any "Trouble Codes" are present. 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 usually requires one week of driving. posted by SmogTips Support

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