From what make and model vehicle? And yes, they are active, feeding an
amplifier and pulse shaper to provide a final RPM value to the TCM.
I was not told what its from. Googling I only found references to overdrive
inhibitor switches not tachometer type sensors. So a standing 12V across
them ?
"N_Cook" <div...@tcp.co.uk> wrote in message
news:j0gq81$5mm$1...@dont-email.me...
I think you should ask this question in uk.rec.cars.maintenance instead.
Lots of very knowledgeable people there.
Gareth.
Your description is an inductive tachometer pickup coil... I don't think you
will find any biased with 12 volts across them either.
I hope gearboxes make good Faraday screens against ignition EMI, there is no
braid screening around the signal wires though.
Generally twisted pair is used (at least on the ones that I work with), and
I've had little problems with EMI (though I do work primarily with diesel
trucks so EMI won't be ignition based at least). These same transmission
(for me) are used with gas engines however, so it appears to the designer
that EMI won't be an issue.