Just recently every once and awhile I get the Check Engine light on while driving. Trying the key trick I get a code 12 and 21. What I don't understand is that following those codes it gives four flashes, a solid check engine light, four flashes, a solid check engine light, and four flashes. I remember in the past it would give the 55, but this is wierd. I took it to Autozone (they pull codes for free) and he got the same thing, and suggested I take it to a dealer and have them look at it. Does anyone know what this could mean?