OBD CodesWhat it means
The computer knows what the ratio between input and output speed should be in each gear. These codes mean the measured ratio does not match the gear selected. In plain words, the gearbox is slipping in that gear or did not engage it.
Codes in this group
| Code | Meaning |
|---|---|
| P0729 | Sixth gear ratio incorrect |
| P0730 | Gear ratio incorrect (gear not identified) |
| P0731 | First gear ratio incorrect |
| P0732 | Second gear ratio incorrect |
| P0733 | Third gear ratio incorrect |
| P0734 | Fourth gear ratio incorrect |
| P0735 | Fifth gear ratio incorrect |
| P0736 | Reverse gear ratio incorrect |
Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.
What you may notice
- Engine revs rise without the car speeding up
- Delayed or harsh engagement
- Gearbox stuck in one gear
- Burning smell from the fluid
Common causes
Most likely first:
- Low transmission fluid
- Old, burnt fluid
- A faulty shift solenoid or valve body
- Worn clutches or bands inside the gearbox
- A faulty speed sensor giving a false ratio
What to check first
- Check the fluid level and colour if there is a dipstick: it should be red or amber, not brown or black
- Stop driving if it slips badly: slipping quickly destroys the clutches
- Get a diagnosis from a transmission specialist before agreeing to a rebuild
Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.
After the repair
Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.
Related codes
Transmission control system request (P0700), Transmission range (gear selector) sensor (P0705), Transmission fluid temperature (P0218), Transmission input and output speed sensors (P0715), Torque converter clutch (P0740), Shift and pressure control solenoids (P0745), Clutch pedal position sensor (manual gearbox) (P0805). All codes.
Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.