In case of failure of the speedometer, then check up the speed sensor pickup and if faulty, replace it. Check the connection between the speed sensor and speedometer/odometer wiring for bad terminal connections, poor connection points or broken wires, and correct as applicable. If in doubt, fit a known working speedometer to check the car's operation; replace the speedometer assembly if it works as expected. If a car speedometer is intermittently working, inspect the wire harness between the speed sensor and the speedometer, and check its terminals for signs of corrosion, connection looseness, or broken wire; if any of these is present, it has to be cleaned or repaired appropriately; further, if the relevancy of the speed sensor pickup fails to work as is expected, it has to be replaced.