How do you fix 2001 Isuzu Rodeo LS speedometer that is not working?

Most likely, you have a worn speedometer gear. The gear is located on the rear right side of the transmission tail housing. A black plastic sensing unit screws onto a metal receiver that contains the gear. The metal receiver is held in place with a bolt and metal retainer. You will notice that the retainer has a flat edge that indexes on the metal receiver, and the metal receiver has two flat edges. Remove the bolt and retainer, and rotate the receiver so the metal retainer indexes on the other flat edge. This will index the gear in a new location where it is not worn. If this does not fix the problem, your sensing unit may be defective.