Car Trigger Wheels

I work in the automotive repair field as a diagnostician. I've been seeing a rash of issues with trigger wheels/tone wheels and their interaction with hall-effect sensors. Temperature seems to be a factor as in some cases the shutter triggers the hall-effect sensor to switch states while is "cold" (ambient temperature) but then starts failing "hot" (normal operating temperature...say 100C?) or vice versa where the issue surfaces when cold, but starts functioning as expected hot.The principles that lead to Currie Point (not insinuating Currie Point is even getting close to be reached) may be coming into play? The trigger wheels are made of steel.Any ideas as to what may be occurring in that would be temperature related, in a very narrow (relatively speaking) temperature range that is causing issues? Thanks,Matt.
- Matt (age 40)
Minneapolis, MN, USA

Hi Matt- could you tell us more about how those wheels work? Where is the magnet? Are the Hall sensors semiconductor-based? 

Is there a website that describes this, maybe with illustrations?

Mike W.

(published on 09/02/2016)