If both your odometer and speedometer are not working, then it's likely your speed sensor needs to be replaced. These are easily installed and located near the back of your transmission. If only your odometer is busted, then it's likely the gears that turn the odometer have broken.

Is it illegal if odometer not working?

You may drive a car with a broken odometer in most states. If you sell the car, you must inform the buyer that the odometer does not work. Car dealers are subject to strict laws to prevent odometer tampering.

How much does it cost to fix the odometer?

The cost of repairing can run as high as $200 – $500 if you visit a mechanic, and you must make a decision about whether this is the right option for you or not. When your odometer ceases to work, most people assume they must replace the unit, which can get quite expensive.