P0730 — Incorrect Gear Ratio

What it means

The transmission module compares input and output shaft speeds and finds that the calculated ratio does not match the gear it commanded. In practice this means the gearbox is slipping, failed to engage the requested gear, or engaged a different one. It usually comes with flaring engine revs on shifts, jerking, and a switch to limp mode with one fixed gear.

Likely causes (most common first)

1. Low, burnt or contaminated transmission fluid causing loss of line pressure
2. Worn clutch packs or bands slipping under load
3. Stuck or electrically failed shift solenoid
4. Worn valve body, leaking separator plate or a stuck pressure regulator
5. Faulty input or output speed sensor giving a false ratio
6. Worn torque converter or internal mechanical damage such as a failed planetary set

Can you drive with it?

Avoid driving: a slipping gearbox overheats and destroys itself within a few dozen kilometres, so use a tow truck.