Focus (02 reg) - speedometer/electrics

Hi all,
I've just bought a used Focus Zetec 1.8 (first reg July 2002).
All is well, except that sometimes the speedometer goes crazy (it swings between about 60 and 130 when actually I'm only driving 15mph in
traffic!). At the same time the radio volumes suddenly increases - it's as if there's some kind of surge in the electrical system. Engine performance, power steering etc. seems unaffected.
Does anybody have the same problem and/or know what the likely solution will be? I'll be taking it to my mechanic soon but I'd like an idea in advance as to what to expect!
Thanks in advance.
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The volume increase in the radio could be caused by the automatic volume control feature of the radio. It uses the VSS (vehicle speed sensor) to increase volume automatically when driving at higher speeds. Try turning off that feature (on my radio the option is in the menu under AVC) and see if the volume spikes when the speedometer goes crazy again. If the volume doesn't spike, then something might be wrong with the VSS or some VSS connections.
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Dave T wrote:

The speedometer display is driven by the ECU. This takes a value from the VSS (Vehicle Speed Sensor) that is mounted on the transmission. The radio has an option to get louder as you drive faster and this also uses the value from the VSS.
It is very common on older cars (mine included!) for the VSS to fail such that there is no speedo display.
Your problem would seem to be either an intermittent connection, probably at the VSS connector, or interference from another vehicle system. The VSS is fairly inaccessible, and is reached from under the vehicle. If your vehicle is under warranty it should be an easy and quick fix. If you need to do it yourself, or point someone else in the right direction, try Googling in this group for "VSS" or "speedometer" and you will find out lots of info.
If your VSS should need replacing, it costs about 25UKP to buy and some patience to replace. A main dealer would charge up to 100UKP to do it, an independent a touch less. No special tools are needed.
For future reference please let the group know how you get on.
Good luck and enjoy your Focus!
Chris
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Chris Whelan wrote:

Thanks Chris and NoRemorse for your prompt answers! I will let the group know what happens.
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