2004 Buick Rendezvous Check engine soon light

The check engine soon light is illuminated on the digital display not the actual check engine soon light. Also the high beam indicator in the dash cluster shows up randomly and flickers rapidly for a couple seconds then goes out. Just changed the gas cap and the battery to try and illinate any problems, but no luck. Any ideas?

I forgot to mention earlier that I did take it too advanced auto, and autozone as well. No codes were found. That is part of the delima. I also thought that maybe it could have been calling for an oil change. I called the dealer and got the code to turn on the ignition, but not actually start the car, just pump the gas pettle 3 times. So I did that several times and the service engine soon light blinked and would come back on. Is there anything else like the oil changing sensor that would give a service engine soon light. I checked all fluids and made sure they were full. Im clueless.