Intermittent speedometer problem

Twice in the last few weeks I've noticed the speedometer on my 2005 3.5L Santa Fe was not working. A minute later it was fine and did not malfunction
for the rest of the ride. I've noticed this both time getting on to expressways. It did not work until the next time the car came to a stop, then worked fine.
Any idea what the problem is and why it only happens once in a while?
Thanks, Jon
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I've seen three things cause this sort of problem, in order of frequency: 1. Worn speedometer driven gear (on vehicle speed sensor in transmission). 2. Broken/barely touching wire at vehicle speed sensor connector 3. Intermittent problem with vehicle speed sensor itself.
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wrote:

I've seen three things cause this sort of problem, in order of frequency: 1. Worn speedometer driven gear (on vehicle speed sensor in transmission). 2. Broken/barely touching wire at vehicle speed sensor connector 3. Intermittent problem with vehicle speed sensor itself.
Thanks HT. Can you point me to where the speed sensor is located? Maybe I can eyeball it to see if I see an issue.
Also, I was under the impression the speedometer on the 3.5L was electronic. Is that incorrect? Would it still have gears?
Jon
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The sensor is located on top of the differential portion of the transmission.
The speedometer is indeed electronic. The gear and sensor assembly bolts onto the differential of the transmission. A gear on the differential turns a gear on on the sensor assembly, which in turn operates the sensor on the assembly. The sensor then sends a square wave signal via a dedicated wire to the speedometer (and other components).
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