Transmission · Powertrain · generic (SAE-defined)
P0731: Gear 1 Incorrect Ratio
P0731 means the transmission computer detected that first gear is not producing the expected input-to-output speed ratio, which usually indicates first-gear slipping.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0731 sets
When first gear is commanded, the transmission control module (TCM) compares the measured ratio of input to output speed with first gear's design ratio. If they differ beyond an allowed margin for a set time, the TCM sets P0731. On some transmissions engine speed is used in place of an input sensor; the thresholds are manufacturer-specific.
Common causes of P0731
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Low transmission fluid
- Worn first-gear clutch or one-way clutch
- Faulty shift or pressure control solenoid
- Low line pressure from a worn pump or clogged filter
- Sticking valve in the valve body
- Speed sensor providing incorrect data
P0731 symptoms
- Check engine light on
- Slow or slipping acceleration from a stop
- Engine revs rise without matching acceleration
- Delayed engagement into drive
- Transmission starting in a higher gear
How P0731 is diagnosed
- Read all transmission codes and record freeze frame data
- Check fluid level and condition
- Road test from a stop while monitoring input, output and engine speed
- Confirm speed sensor accuracy
- Check solenoid operation and line pressure
- Inspect pan debris and evaluate internal clutch condition
Typical fixes for P0731
- Correct fluid level or service the fluid and filter
- Replace faulty solenoids
- Repair the valve body
- Replace a faulty speed sensor
- Rebuild or replace the transmission if first-gear components are worn
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0731 FAQ
What does code P0731 mean?
P0731 means the transmission computer detected that first gear is not producing the expected input-to-output speed ratio, which usually indicates first-gear slipping. The standard definition is "Gear 1 Incorrect Ratio."
Can I drive with a P0731 code?
Drive as little as possible. Slipping in first gear shows up during takeoff, where loads are highest, so continued driving risks rapid clutch damage and possible limp mode.
Why does P0731 feel worst when pulling away?
First gear handles takeoff, when torque demand is highest. Any slipping in first is most noticeable as the vehicle starts moving.
Can a sensor cause P0731 without real slipping?
Yes. If the input or output speed sensor reads incorrectly, the calculated ratio will be wrong, so sensor data should be verified first.
Keep researching
More transmission codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.