OBD-II Code · Transmission
P0731
Gear 1 Incorrect Ratio
First gear ratio fault.
Common symptoms
- Check engine light
- Slipping in 1st
Likely causes
- Worn 1st gear clutch
- Solenoid
- Low fluid
Where to start
- Try the cheapest cause first. Start by checking: worn 1st gear clutch.
- Cost & scope. $500-$3,500
- If the code returns after the fix: escalate to a shop or scanner with live-data and freeze-frame. A code that re-sets means the underlying fault is still there. Don't keep driving with this one active — risk of damage.
Read the full diagnostic procedure
P0731 is the gear-specific version of P0730 — the TCM has commanded 1st gear but the actual input-to-output ratio doesn't match what 1st should be (typically around 2.8-3.5:1 on most automatics). That means 1st gear is slipping, or the wrong gear actually engaged, or a shift-solenoid valve has stuck. Fluid level and color first; burned fluid plus a P0731 on a higher-mileage trans is usually a slipping low/reverse clutch or a failed forward-clutch seal. With the trans in DRIVE at a stop and the brake held, watch input RPM as you brake-torque to ~1,500 RPM (stall test) — input should follow engine RPM closely with minimal slip on a healthy unit. A 200+ RPM gap between engine and input RPM under stall is the smoking gun for converter or clutch slip. Cheapest external causes to rule out first: stuck shift solenoid A or B (often $50-150 each), a stuck pressure-control solenoid, or a valve-body separator-plate failure (the gasket between the valve body and case can fail and cross-feed pressure between circuits, mimicking internal damage for $300 worth of parts).
Vehicle-specific patterns
Vehicle-specific patterns: 2001-2007 Nissan Pathfinder/Frontier with the RE5R05A 5-speed throws P0731 from a known 1st-gear clutch pack failure — Nissan TSB and class-action coverage on certain VINs, but past warranty you're rebuilding. 2004-2010 Toyota Sienna/Highlander V6 with the U151E/U660E 5/6-speed rarely throws P0731 unless fluid was neglected past 100k miles — when it does, the cause is usually a worn 1st-gear band servo, not a hard-part failure. 2007-2014 Chrysler/Jeep with the 545RFE/65RFE throws P0731 from a failed Underdrive Brake assembly when the solenoid-pack drops pressure — solenoid-pack-first diagnostic order saves customers a rebuild quote about 30% of the time per ATRA bulletins. 2005-2010 GM 4L60E/4L65E (Silverado 1500, Trailblazer) throws P0731 from a worn 1-2 accumulator piston or a cracked sun-shell — both internal but the sun-shell failure is catastrophic and often produces metal in the pan. Estimated repair: $300 (solenoid pack) to $3,800+ (full rebuild).
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