P0730 P0xxx · Powertrain (P) High severity
Incorrect Gear Ratio
The ECU compares input and output shaft speeds and finds a ratio that does not match the commanded gear — the transmission is slipping.
Severity guidance: High — stop driving and diagnose now; risk of further damage
Symptoms you will notice
- Slipping between gears
- Flaring on shifts
- Limp mode
- Burnt-fluid smell
Common causes
Ordered from most to least likely — start at the top.
- 1 Low or burnt automatic transmission fluid
- 2 Worn clutches or bands
- 3 Faulty solenoid or valve body
- 4 Failed speed sensor giving bad data
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Check fluid level and condition first — burnt smell and dark colour confirm internal wear.
- ✓ Compare input and output speed PIDs against the expected ratio per gear.
- ✓ Rule out a sensor fault before condemning the gearbox.
- ✓ Line-pressure test if the manufacturer provides a tap.
Repair options
- Fluid and filter service for early slipping
- Solenoid or valve body repair
- Transmission overhaul if clutches are worn
P0730 — frequently asked questions
Is a fluid change enough? +
Only if caught very early. Once the fluid smells burnt the clutches are already damaged.
Can a sensor cause this code? +
Yes — bad speed data produces a false ratio. Always verify with live data before a rebuild.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.