2005 Chrysler 300 CHECK ENGINE LIGHT

2005 Chrysler 300 6 cyl Two Wheel Drive Automatic

I OWN A 2005 CHRYSLER 300. MY CHECK ENGINE LIGHT COMES ON AND GOES OUT EVERY NOW AND THEN. I WENT TO HAVE IT CHECKED OUT AND THE TROUBLE CODE IS P0406. THE MESSAGE READS: THE PCM HAS DETERMINED THAT THE VOLTAGE SIGNAL FROM THE EXHAUST GAS RECIRCULATION SENSOR "A" IS TOO HIGH FOR THE CURRENT ENGINE OPERATING CONDITIONS. WHAT WOULD BE THE BEST CORRECTIVE ACTION TO TAKE, ALSO I USE 87 OCTANE GAS, WOULD THE 89 OCTANE MAKE A DIFFERENCE. THE OWNERS MANUAL CALLS FOR 89, BUT WHAT IS THE DIFFERENCE BEWEEN TWO OCTANE LEVELS.