Hyundai Repair: 2002 hyundai accenct, speed sensors, gear ratios

Question
Have a fault code PO734 stateing wrong 4th gear ratio . What causes this code to come up, it had the right ratio when it left the factory.     Thanks

Answer
Effectively, this code means that the transmission computer thinks the transmission is slipping in fourth gear.

The transmission computer is preprogrammed with the gear ratios of your transmission.  If the ratio of the signal from the input speed sensor to that of the output speed sensor is significantly different from the programmed gear ratio, the transmission computer will set a diagnostic trouble code P073x, where x typically represents the gear that has the wrong ratio.  In your case, P0734 indicates fourth gear.

If you have a P0717 or P0722, you should investigate the problem with them first, as these are codes for the speed sensors.  If the speed sensors are not working correctly, a gear ratio code may be erroneously stored.  If you have no codes other than P0734, chances are there's a significant problem inside your transmission.