Via 125 Speed display erratic

Oct 10, 2014
TomTom Model(s)
Via 125
Hi, I have a Via 125 and am finding the speed that is displayed to be very erratic, sometimes it shows the speed correctly, at other times it will vary, anything from 5 to 30 kmh different to what speed I am traveling at. It usually displays a speed lower than I am doing. I compare it with both my speedo & my Garmin Gps which both hold closely to the cruise control setting.
Any help would be appreciated. Thanks.
The speed shown in any gps is normally accurate while speedos are purposely designed to show a speed that may be as much as 10% greater than reality -- depending upon manufacturer.

But a fluctuation as you describe (up to 30 mph) should not be happening. Certainly unusual. If you are keeping the Via right next to the Garmin while driving, try separating the two devices a bit.
Thank you dhn, I am very aware of the inaccuracy of speedo's which is why I rely on my Tom Tom for accurate speeds. The variations I get usually indicate a slower speed than I am actually traveling which is a worry with law enforcement. It will often be correct then will fluctuate down by 8-15kmh & come partway back then drop again, it goes all over the place. The greatest variation I have seen is about 30kmh (19mph) My Garmin is mounted 450mm (16") from the Via, neither unit uses external antennae, Via is windscreen mounted while the Garmin is mounted on the dash. I usually only use the Gamin for recording my off road journeys. Any more advice?
The only reason that this should happen is if the GPS lock is poor and the device isn't able to accurately track the difference in your position vs. time. What does the satellite view tell you about signal quality when this occurs? Did this just recently start to be a problem?
Hi again, yes this problem is intermittent & you may be on to something here, Recently I had the problem again & checked signal strength which was 79% & 9 satellites locked, but seemed stable, not fluctuating. I was traveling in timbered country at the time - not sure if I this was the case on previous occasions. I have just completed a couple of thousand Ks across the Nullabor Plain with no apparent problem, What is an acceptable signal strength & can an external antenna be used with this unit? Thanks for your input.

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