I have a Engine System Service Required message on my 1999 Volvo S-80 T6. I stopped by Auto Zone to see if they could pull a code from the computer. They used an Actron scanner and it came back without any codes. What can I use to get the code that is triggering the Engine System Service message? The message clears after 5 key cycles and then comes back a few days later.

 

I have the samemessage comming on intermittantly amongst my othermessages but it only comes on right after start up, if I turn the car off and restart themessge is gone.