P0731Gear 1 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. P0731 concerns first gear. A 2006 GM table uses a tighter 4 % limit here and caps output speed at 1260 rpm; Saab's 2002 9-5 flags 3 % with the brake released. With a one-way clutch in first, slip shows as slipping when pulling away. On GM manual transmissions it checks the gear position sensor instead.
- What you may notice
- Slipping or flare in first 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 or brake for first 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: €100 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.