P0729 Gear 6 Incorrect Ratio

P0729 indicates gear 6 incorrect ratio. The controller sees input and output speed relationship that does not match the expected sixth gear ratio.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not authorize major transmission work from a single ratio code without checking speed sensors, solenoids, pressure, and fluid first.

Symptoms of P0729

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0729

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Compare commanded gear, actual ratio, input speed, output speed, shift timing, pressure data, and fluid temperature.
Check fluid level and condition, solenoid command, pressure-control behavior, and speed sensor plausibility.
Review whether the ratio error occurs only in sixth gear, under load, when hot, or during the shift into sixth.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.