There are some codes that will set but not turn on the check engine light.Generally they don't effect emissions or signify a serious problem. Case in point: I work on Hyundai's also.I had one came in that didn't run right.Check codes and it shows a code for a knock sensor malfunction and the codes has set over 200 times but no engine light.Come to find out a rodent had chewed the wires in half....
And specifically chrysler... I know some SKim codes won't urn on the check engine light.... there are others but you get the picture
