P0729Gear 6 Incorrect Ratio
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- The transmission module divides input (turbine) speed by output speed and compares the result with the ratio of the commanded gear; a deviation means slip – a clutch or brake not holding, too little pressure – or a wrong gear. Thresholds: Ford more than 30 rpm off for 1.8 s three times (diesel 2023: over 20 % for 12 s), GM's 2006 tables and the Allison 1000 converter slip of 200–230 rpm for 2.25 s after one trip, Saab's Aisin boxes over 20 % twelve times without MIL. P0729 concerns sixth gear. Saab's Aisin six-speed also checks whether the actual ratio matches fourth or fifth – the sixth gear clutch is not holding and the box drops into another gear. Ford stores it only if the fault does not fit a particular solenoid (otherwise P0751 ff). On GM manual transmissions (LT4) it checks the gear position sensor instead.
- What you may notice
- Slipping or flare in sixth gear, engine speed higher than expected
- Harsh or delayed shifts
- Limp mode (Aisin: second gear and reverse only), transmission warning
- Check engine light depending on manufacturer
- Likely causes
- LikelyFluid level too low or fluid worn or contaminated
- LikelyClutch for sixth gear worn (linings, piston seal)
- PossibleSticking shift or pressure valve, leaking valve body gasket, blocked passages
- PossibleGM manual transmissions only: gear position sensor faulty or not learned
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.