2000 S80 message display?

I have a 2000 S80 T6 that runs good, but after it is warm and you turn the engine off, when you restart it while still warm I usually get a message that says "ENGINE SYSTEM SERVICE REQUIRED" and the little triangle in the middle of the gauges is orange. When I check for codes there are none, but when I erase for codes it will clear the message. WHat does this message mean??? Also once in a while a message that the DTSC needs serviced, what does that mean?
Thanks