The speedometer is required by law.
The Tachometer is a good idea as it indicated the engine speed in RPM (revolutions per minute) and allows you to monitor the engine in a very quiet car or over modern stereos.
check the fuses.
its probably a blown fuse or relay
If they have both failed at the same time it sounds like a power supply problem. Check fuses
fuse to the dash gone ???
The speedometer and rev counter (tachometer) on a Volvo V40 function through electronic signals generated by the vehicle's sensors. The speedometer receives data from the wheel speed sensor, which measures the rotation of the wheels, while the tachometer gets input from the engine control unit (ECU), which monitors engine RPM through the crankshaft position sensor. These signals are then processed and displayed on the dashboard gauges, providing real-time information to the driver.
the speedometer is based off of a gear in the tranny that spins.
The speed sensor on the trans.
Use a GPS ^ posted by someone else What you want to do is drive with traffic and watch your tachometer. That is the RPM gauge, if your car has one. By marking the tach you can tell your approximate speed at any given time. You need to watch what RPM's you shift at, if you are in fifth gear cruising at 55mph then look at where your RPM's are... they will always be really close that in 5th gear at 55mph. You can then use that as an easy way to tell your speed with a broken speedometer.
Hi There, On my 1995 Nissan Pick-up, The speedometer as well as the tachometer would intermittenly stop working. Sometimes one would work then the other would stop working, sometimes both stopped working at the same time. I never knew when it would happen. Then, at 90,000 miles, the Check Engine light came on and everything worked GREAT. It turns out that the wire that sets off the Check Engine light was shroting out causing the problems. It was fixed today for a cost of $160.65. It worked for me, I hope that it works for you. Good Luck!
Have vehicle scanned to determine the problem
Family commitments
The logical problem - would be a broken speedo cable. The speedo & odometer are both run from the same cable.