Powertrain, generic · Transmission

P0731 Gear 1 Incorrect Ratio

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

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

Symptoms

  • 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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–3,500
Time0–14 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Check fluid level and condition
  2. Check for related solenoid codes
  3. Have the transmission inspected

Parts involved

transmission clutchestransmission valve bodytransmission fluidtransmission control module

Related codes

P0730P0732P072CP0751P0716P0721

References: saabwisonline.com, saabwisonline.com, saabwisonline.com, gsi.ext.gm.com.