When the drive cycle has not been completed there will be a code P1000. Once the drive cycle has been completed that code goes away. When reading the codes is required for a smog test, the drive cycle must have been completed. If the drive cycle has not been completed, there could be a problem that the OBD II system hasn't done the test for yet. Two examples are the cat effeciency and fuel evap leaks.
When you clear the other codes, the P1000 is present until the drive cycle is completed. The same thing happens when the battery is disconnected.
