Code 12 will always be present IF your ride is running right.
It's simply an RPM reference signal sent to the ECM to show
you that the dist is indeed sending a signal. If it didn't show
this code when going into the diag mode, it spells trouble,
unless the lite is burned out for those you use the "ses"
to count codes. All is good, if all you get is a code 12 three
times and a code 55 at the end of the data stream..Code
55 being the ID code letting you know that the diag code
retrieval is finished..Now some rides will just go the 12 code
over and over, others the 55 code. Anything in between are the
trouble codes. This mostly pertains to CCC and OBD I Platforms.