Speed Sensors?

[RyanZ71]

Last time I had my truck in for service they were unable to duplicate the problem with my overdrive cutting out on me for several min after driving at highway speeds for 15+ min, usually while it is hot out. They said it seems to shift just fine. It only happens every once in a blue moon, not all the time. They mentioned it could be a bad speed sensor. What exactly is a speed sensor, where is it located? How does it work?

[OnyxMAX]

typicly there are 5 sometimes less depending on traction control ABS irs solid axle.

 

one at each wheel, or each front wheel and one in the rear diff, and one on the transmission outputshaft.

 

normaly the transmission one is the main vss(vehicle speed sensor), and the others are called wss(wheel speed sensors).

 

the vss runs the spedo and in conjunction with the crank sensor can tell when the tranny slips.

 

the wss activate traction control, on the rear activate the G80, tell the computer to modulate the ABS, monitor tire pressure through wheel rpm.

 

it works by generating a frequency. a magnet is wired up and positioned a set distance from a notched ring.as the ring turns the peeks and valleys move the magnetic field and generate a curent (like a alternator) the computer in control decodes the wave (frequenncy) and gives a speed readout.

 

generaly if the vss and wss start reading different things a code gets set.

 

i'v never heard of the vss causing overdrive lockout though. only reason i could see that happening is if the overdrive was slipping badly. but that should activate limp mode.