P0731: Gear 1 Incorrect Ratio

What does P0731 mean?

The ratio between transmission input and output speed does not match the expected ratio for first gear. The code can reflect real clutch slip, hydraulic/control trouble, or unreliable speed data; it does not identify a specific failed internal part.

Generic OBD-II definition: Gear 1 Incorrect Ratio. Confirm applicability in your vehicle service information.

Common causes

• Low or degraded transmission fluid
• Valve-body or pressure-control problem
• Worn internal clutch/band or other mechanical fault
• Shift-control or speed-sensor fault

Symptoms

• Sluggish takeoff or starts in a higher gear
• Transmission slipping
• Check engine or transmission warning

Diagnostic focus

Compare commanded first gear with input/output speeds at takeoff. If several ratio codes occur, check shared pressure and speed inputs before blaming one first-gear clutch.

Can I keep driving with P0731?

Severity: High Avoid towing, steep loads, and prolonged driving until diagnosed. Stop and arrange recovery if the transmission slips, loses drive, overheats, or bangs into gear; driving through slip can cause further damage.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Check fluid level and condition using the transmission-specific procedure
• Diagnose associated speed-sensor and solenoid codes first
• Have commanded gear, actual ratio, and hydraulic pressure checked

Sources & review

• OBD-Codes.com: P0731
• TroubleCodes.net: generic code definitions

Definitions and diagnostic background checked 2026-11-06. Generic guidance, not a substitute for the service procedure for your exact year, engine, and transmission.