Nebaukanezzer wrote:
?are/can these codes generated without CEL's or is there always a CEL when a code is produced?
  I've seen conflicting acocunts of just what the rules are, but apparently, there are some faults which are regarded as serious enough that the CEL will light up as soon as one is detected, but most faults are considered much less severe; for these, when such a fault first occurs, a Pending Trouble Code (PTC) is set, which can be retrieved via an OBD?II scanner, but which does not light the CEL.  After some amount of time, or some number of siuccessful drive cyles, if the fault is not repeated, the PTC clears, and the driver will never have known that it had occurred unless he had retrieved it via an OBD?II scanner.  If, while the PTC is still active, the fault occurs again, then the PTC becomes a Diagnostic Trouble Code (DTC), and the CEL lights up.

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Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX.  No mods. (Well, OK, one mod.  Before I got rid of my previous car, a 1994 Tempo, I swapped radios.  I liked the Tempo's radio better.  That counts as a mod, doesn't it?  I also kept one of my Tempo's wheels to use as a spare.  I hate those stupid ?compact? spares that come with modern cars.  Does this count as a mod?  If so, I guess I have two mods.  Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)