P1491 is for the radiator fan relay. Whomever told you emission problem misinformed you. They must have been thinking about P1451.
If the coil pack has never been replaced, I would do that before you do any other diagnostic. But if it has been replaced, I would check to make sure that it is still within spec.
Here is the procedure for P1491.
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Wednesday, February 11th, 2009 AT 12:33 AM