Has this happened to anyone else??? Daughters car was running bad (see SC300 Spark Plug thread by me), and the tach stopped working. I got it running great tonight, and while on a test drive (running it thru the paces) the tach starts working. It did this once before right before the Variable Voltage Fuel Pump took a dump. Same thing, Tach stopped one day before car would not run, fixed voltage regulator and Tach starts working again until this past incident. Just curious......

Jim

 

Similar issue with my son's '92 SC400, but the speedo function is also intermitent. I haven't really fixed the problem yet, but some members indicate a good whack to the top of the dash above the instrument panel sometimes works. Not the mechanical solution you might be looking for, but it worked only temporarily for us. Supposedly it loosens up a sticky needle motor.
https://www.clublexus.com/forums/per...tent-tach.html

 

this "wack" works for me when the occasional stuck needle happens.

 

I think it may be a way for the computer to tell you...."Hey, the car is NOT running correctly...". Sort of a warning that the car needs to be checked out. I think it is the cars way of telling us something is wrong. Just a theory.....

Jim