Bumping an old thread here. I switched out the left and right rear speed sensors over a year ago and have gotten occasional trifecta lights sometimes with the speedo not working and most times with the speedo working. I believe the brand of the sensors was Febi but not certain. Is there an ohms value that defines a properly working sensor? Can I spin the wheel and see variability in the reading on a properly functioning sensor? This may also be a correct indication of another problem I'm having either with a binding caliper, a front diff or a transfer case issue.