Does obd scanner remove check engine light only or doers it also removes unfixed codes from memory?

Question

If you use an obd reader to to delete the check engine light for a problem which hasnt been fixed, the check engine light will eventually come back on. My question is, regarding the code that is on memory, will that also go when you delete the code and come back on later for an unfixed problem or will it always be present until the problem is fixed?

Put it another way, let's say you are buying a car, if the seller deletes all codes just before the buyer arrives, will the buyers obd reader not see the codes?

Or if the buyer puts his obd reader in, will this reveal all the codes(i.e. they are permenantly there until fixed and deleted and its only the check engine light that temporarily goes)?

Thanks

Answer 1

It depends on the year. From model year 2010, some codes are now permanent, meaning a scan tool can not clear them.

https://www.autoserviceworld.com/carsmagazine/taking-a-first-look-at-permanent-dtcs/

For 1996 to some 2009 model years, the code is completely cleared from memory. But if you are looking to buy an older OBDII vehicle, you can check to see if all of the monitors are complete and if they have passed or not. Any incomplete monitors may indicate a recent code clearing event.