P0729: Gear 6 Incorrect Ratio

What does P0729 mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• 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

Common causes

• High Fluid level too low or fluid worn or contaminated
• High Clutch for sixth gear worn (linings, piston seal)
• Medium Sticking shift or pressure valve, leaking valve body gasket, blocked passages
• Medium GM manual transmissions only: gear position sensor faulty or not learned

Likelihood is a general estimate across vehicles; your make and model may differ.