Answer to: speedometer sometimes work,at times it does notCheck the grounds for the dash panel. Also, unplug, clean and replug the various plugs leading from the dash panel to the rest of the car. If you notice any that seem sloppy (loose), have burned places, or are heavily corroded, replace them.
Answer to: Tire Pressure Light is on even though the tires don't need air.The sensors contain batteries that are good for 3-5 years, depending on the units used. This is a nearly universal design element - all makes and models. Take it to a reputable tire shop to have the batteries replaced.