P0730: Incorrect gear ratio
The automatic gearbox’s input and output speeds don’t match the gear it’s in: it may be slipping, or a speed reading is wrong.
Updated
What P0730 means
An automatic gearbox knows the ratio of each gear. Its control module compares the speed going in, from the engine, with the speed coming out. If the two don’t match the selected gear, the gearbox is slipping, or one of the speed readings is wrong.
P0730 says this happened without naming the gear; codes such as P0731 to P0735 name gears 1 to 5.
P0731 to P0736: the ratio wrong in one gear
These codes name the gear in which the ratio was wrong: P0731 first gear up to P0735 fifth, and P0736 reverse. The causes, the advice and the checks are the same as for P0730. A slip in one gear only can point to the clutch or band that engages that gear, or to the solenoid that controls it.
P0731: Gear 1 Incorrect Ratio
The automatic gearbox’s input and output speeds don’t match one particular gear: P0731 to P0735 name gears 1 to 5, P0736 reverse. It may be slipping in that gear, or a speed reading is wrong.
Common causes: low or worn-out gearbox oil, faulty shift solenoid or valve body, worn clutches or bands inside the gearbox, faulty gearbox speed sensor.
P0732: Gear 2 Incorrect Ratio
The automatic gearbox’s input and output speeds don’t match one particular gear: P0731 to P0735 name gears 1 to 5, P0736 reverse. It may be slipping in that gear, or a speed reading is wrong.
Common causes: low or worn-out gearbox oil, faulty shift solenoid or valve body, worn clutches or bands inside the gearbox, faulty gearbox speed sensor.
P0733: Gear 3 Incorrect Ratio
The automatic gearbox’s input and output speeds don’t match one particular gear: P0731 to P0735 name gears 1 to 5, P0736 reverse. It may be slipping in that gear, or a speed reading is wrong.
Common causes: low or worn-out gearbox oil, faulty shift solenoid or valve body, worn clutches or bands inside the gearbox, faulty gearbox speed sensor.
P0734: Gear 4 Incorrect Ratio
The automatic gearbox’s input and output speeds don’t match one particular gear: P0731 to P0735 name gears 1 to 5, P0736 reverse. It may be slipping in that gear, or a speed reading is wrong.
Common causes: low or worn-out gearbox oil, faulty shift solenoid or valve body, worn clutches or bands inside the gearbox, faulty gearbox speed sensor.
P0735: Gear 5 Incorrect Ratio
The automatic gearbox’s input and output speeds don’t match one particular gear: P0731 to P0735 name gears 1 to 5, P0736 reverse. It may be slipping in that gear, or a speed reading is wrong.
Common causes: low or worn-out gearbox oil, faulty shift solenoid or valve body, worn clutches or bands inside the gearbox, faulty gearbox speed sensor.
P0736: Reverse Incorrect Ratio
The automatic gearbox’s input and output speeds don’t match one particular gear: P0731 to P0735 name gears 1 to 5, P0736 reverse. It may be slipping in that gear, or a speed reading is wrong.
Common causes: low or worn-out gearbox oil, faulty shift solenoid or valve body, worn clutches or bands inside the gearbox, faulty gearbox speed sensor.
Can I keep driving?
Drive gently
Drive gently and only as far as you need to, and have it checked soon. A slipping gearbox wears faster with every drive, and it may stay in one gear (limp mode). If it slips badly or won’t drive, don’t force it: have it recovered.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
Many gearboxes switch to a limp mode with this fault, staying in one gear. Read My Car shows codes from the gearbox module next to the engine’s, where the car shares them over generic OBD2.
Symptoms
- The engine revs rise without the car speeding up (slipping).
- Harsh, late or missing gear changes.
- Stuck in one gear, or a gearbox warning on the dashboard.
Common causes
- Low or worn-out gearbox oil. Too little or old oil lets the clutches inside slip. Many gearboxes have no dipstick, so checking the level needs the procedure for your gearbox.
- Faulty shift solenoid or valve body. They steer the oil to the clutches. One that sticks gives the wrong gear, or a slip.
- Worn clutches or bands inside the gearbox. Internal wear usually means an overhaul or a replacement gearbox.
- Faulty gearbox speed sensor. A wrong speed reading can make a good gearbox look as if it slips.
Typical fixes
- Read all codes, including any the gearbox module reports.
- Have the gearbox oil level and condition checked, as the service information for your gearbox describes.
- Have the speed sensors, the shift solenoids and the valve body checked.
- If the oil and controls are fine, have the gearbox inspected for internal wear.
Questions
Can I drive with P0730?
Gently, and only as far as you need to, and have it checked soon. A slipping gearbox wears faster with every drive. If it slips badly or won’t drive, don’t force it: have it recovered.
Can a gearbox oil change fix P0730?
Only if low or worn-out oil is the cause. If the clutches inside are worn, new oil doesn’t repair them. Have the level and condition checked first.