Easy to set DTC

I am working with vehicle diagnostics and CAN, but have run into a problem when trying to do testing. There is nothing wrong with the vehicle I am using. I need to find either a harmless and very likely easily reversible problem I can create on the vehicle that will set a trouble code for me to read, or I need to find a way to artificially set one. I am actually not even sure the latter is possible. I know there are plenty of things I can do to cause trouble with a vehicle, but I am trying to find something that won't permanently damage the vehicle.

I know Trouble codes aren't universal across all vehicles, or at least not all of them are, I just figured that there must be some common problem that most vehicles will set a DTC for.