He is not asking about codes. He is needing his readiness monitors to run to pass emissions testing. The test stations got used to folks clearing codes to take the test and with OBDII testing all the monitors except maybe one or two need to have been performed successfully in order to pass the emissions test. Every time you clear codes you also clear the monitor test results, so if you have an emissions test coming up the car will have to be driven till they reset pass the monitor tests.

Being in a no emissions state I have very little experience with this issue, but I know from working on the systems that many of them will not even do the test unless certaing conditions exist. The evap monitor won't run if the tank is too full or too empty EVER. It also won't run if you are above a certain altitude. The cat monitor may take hundreds of miles to run if ever on a early OBDII car. There are recommended drive cycles to get the monitor tests to run but they are critically sensitive and the criteria is more than just the drive, with altitude, road condition, fuel level, etc, etc, aslo being part of the testing criteria.

I have heard of numerous pre 2000 cars that had to get exemptions because the monitors just would not run.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician