Heat oven to 350°F. Grease 13x9-inch pan. Reserve 2/3 cup of the dry cake mix for filling. In large bowl, combine remaining dry cake mix, margarine and 1 egg; beat at low speed until well blended. Press in bottom of greased pan. Bake at 350°F. for 15 to 20 minutes or until light golden brown.
Meanwhile, in large bowl, combine reserved 2/3 cup dry cake mix, brown sugar, corn syrup, vanilla and 3 eggs; beat at low speed until moistened. Beat 1 minute at medium speed or until well blended.
Remove pan from oven. Pour filling mixture over warm base. Sprinkle with pecans.
Return to oven; bake an additional 30 to 35 minutes or until filling is set. Cool 1 1/2 hours or until completely cooled. Cut into bars. Store in refrigerator.