speedometer malfunctions

Occassionally my speedometer will go to 0 and then within a few seconds (or up to a minute) will start working. Iíve only noticed this when Iím on the freeway adjacent to the airport except for one
time when I was close to a hospital after passing a motorcycle policeman who had stopped a car. Wondering if some radio or electronic signal could cause this or is it something else.
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Here's a copy of my post and the reply from about a year ago: My out-of-warranty 2002 XG350's speedometer quit working on the way home from work the other day. All of a sudden it was reading 0 mph. The tach was still working, and the car seemed to be running fine. After noticing this, I was just about to engage the cruise control to see if that was working or not, when the speedometer jumped back to life and has been working ever since. Anyone seen this behavior before, or know what to do about it?
Reply from HyundaiTech:
Usually, the problem is with the vehicle speed sensor or the gear attached to it. It's nearly impossible to tell which is faulty without trial and error, so I usually just replace both at the same time-- they're part of the same assembly.
I bought the speed sensor and gear from the Hyundai dealer and then ran into trouble installing them. The old one is in really tight and, not knowing exactly how things fit together, I sure didn't want to break the speed sensor off in the tranny, so I went back to the dealer to have it installed. They wanted to charge me $35 to "diagnose" whether it was the speed sensor or not, but I insisted they just install the sensor. It worked, and I haven't had any trouble from it since.
Dan
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