P0731 means Gear 1 Incorrect Ratio. In first gear, the ratio between input and output shaft speeds does not match what first gear should produce, which usually means a clutch or band applied in first gear is slipping. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0731 means
Electronically controlled automatics are run by a transmission control module (TCM), a separate box or part of the engine computer. It reads speed sensors, the range sensor and fluid temperature to decide when to shift, and drives solenoids that apply clutches and the torque converter clutch. Many basic code readers only show the generic P0700; a scan tool that reads the transmission module shows the specific fault. Check fluid level and condition first, since low or burnt fluid causes many transmission codes.
P0731 symptoms
- Engine speed flaring in first gear
- Delayed or harsh shifts
- Limp mode
- Burnt fluid smell
Common causes of P0731
- Low or degraded fluid
- Worn clutch pack or band used in first gear
- Worn or failed low one-way clutch (sprag) on many transmissions
- Low line pressure from a worn pump, a clogged filter or a pressure control fault
- A faulty input or output speed sensor giving a false ratio
How to diagnose P0731
- Check transmission fluid level and condition first
- Confirm both speed sensor signals are clean before trusting the ratio
- Watch input and output speeds in first gear on a scan tool
- Check line pressure with a gauge
- Inspect the pan for friction material and metal
Can you drive with P0731?
Limit driving: slipping in first gear builds heat and debris quickly.
P0731 tips
On many automatics first gear depends on a one-way clutch (sprag). A classic sign of a failed low sprag is no movement, or a flare, in drive from a stop while the manual low range still pulls; that pattern with P0731 points to the sprag rather than a solenoid.
Will P0731 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0731 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0730 | Incorrect Gear Ratio |
| P0732 | Gear 2 Incorrect Ratio |
| P0715 | Input/Turbine Speed Sensor A Circuit |
Guides that help
When it is more than a sensor
If the fault turns out to be internal (worn clutches, a failed converter or a damaged valve body), compare a rebuild with a replacement in transmission rebuild vs replacement and transmission replacement cost, identify your unit with what transmission do I have?, and browse our transmissions.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.