I talked with the dealer about this a few years ago. They said that the bulbs should be replaced as sets. I didn't want to waste time when one of my stop lights burnt out. I replace every single bulb in the back including the one everone forgets the center stop light with sylvania "oem". They worked perfectly. I think the computer must be checking and comparing the resistance of the bulbs and of they don't match, the warning light lights up even when the bulbs are working fine....just a thought...good luck