P0734: Gear 4 Incorrect Ratio

What does P0734 mean?

The ratio between transmission input and output speed does not match the expected ratio for fourth 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 4 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

• Failure to engage or hold fourth gear
• Transmission slipping
• Check engine or transmission warning

Diagnostic focus

Do not assume fourth gear always means overdrive; ratios vary by transmission. Use the exact transmission identification and gear chart when reviewing input/output data.

Can I keep driving with P0734?

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: P0734
• 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.