What does P0730 incorrect gear ratio mean?
Short answer: The transmission computer compared input and output speeds and found the ratio did not match the commanded gear, which usually means slipping clutches, low or worn fluid, a solenoid problem or a speed sensor fault.
An automatic transmission computer knows which gear it commanded and calculates the ratio from input and output speed sensors. If the actual ratio differs, it sets P0730, sometimes with a gear-specific code. The transmission may go into a failsafe gear.
Check fluid level and condition first, using the procedure in service information, which often requires a specific fluid temperature. Burnt or debris-laden fluid suggests internal wear. Look for other codes, especially speed sensor and solenoid codes, which can cause a false ratio code.
Review live data for input speed, output speed, commanded gear and line pressure if available. Road test to see which gear shows the error. Some transmissions need adaptations reset after repairs. Raise and support the vehicle safely on a lift or stands if you need to check the fluid underneath, and be careful around hot fluid and exhaust.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.