What causes speed odometer malfunction ? on 1998 Volvo S70

When I drive off at a low speed I stand a chance of the speed odometer working
until I come to a stop. If I pull off at a moderate speed the speed odometer will not work. What do you think causes this malfunction?

2 answers 2 comments
There's a sensor which works with the speedometer you need to replace that sensor
The speedometer receives a vehicle speed signal from the ABS Control Module. If the speedometer is not working, I would look at the ABS module (very common on this vehicle) for faults and address that first. Have you had a problem with the ABS lights coming on?
If there are other electrical issues at the same time, like the radio not working or the dash lights not working, then the electrical portion of the ignition switch may be having issues, which is another common problem on this Volvo.
Answer#1Reply: I need to say that the ABS light comes on along with the trac light. Sometimes the lights would go
out, but will come back on as if someone flicked a switch. For the most though those lights stay illuminated throughout the operation of the car.
Then the ABS Control Module is likely your issue. Like I say, it is very common complaint not only to Volvo, but many other vehicles as well. There are even companies who repair these modules, see this: http://www.modulemaster.com/en/abs/ate_mk20.php
Good Luck!