On my 2013 Silverado a few months ago I got a check engine alert that mo. 7 fuel injector needed service. There was an occasional miss when the truck idled, but never constant. Then the check engine light would often go away, and a month later come back. I never could get to it. Now I'm getting a fairly regular P015B & D code with the check engine light on. Is this because of the fuel injector, or could both sensors be off at the same time? Or something else. Thanks for your advice!