How to Repair a Digital Speedometerby Michael Wallace
Unlike a standard speedometer, if a digital unit isn't functioning properly you can troubleshoot it without opening it up. Rather than disassembling it, there are ways to reset and program it which could fix bugs or other problems. The best part is that you don't need to know much about electronics in order to do it.
Open the hood of your car and locate the speedometer gauge cables according to the user manual of your particular automobile. Check the gauge cables to make sure they are properly plugged into the ports on the back of the speedometer. If this doesn't solve the problem proceed to the next step.
Locate the "Function" button on the front of the speedometer and press and hold it while simultaneously turning the engine on. The speedometer will then enter the function menu.
Press the "Function" button repeatedly and scroll through the options until you come to the "Auto" heading.
Press and hold the "Function" button until "-" is displayed on the screen. Release the button and "Unit" will be displayed on the screen.
Wait until a line of zeroes appears on screen and then drive your car around until one mile clicks over. Stop the car and press the function button again. You speedometer is now re-calibrated and this can fix many errors you may be having with the unit.