P0731: Gear 1 Incorrect Ratio
The transmission is not producing the expected gear ratio in first gear, which usually means slipping.
What P0731 means
P0731 narrows an incorrect ratio fault to first gear. The transmission computer commanded first and then divided input shaft speed by output shaft speed. RepairPal explains that it sets when the RPM difference in first gear is greater than allowed, which often implies slipping. First gear handles the highest torque, so worn clutches or bands often show up here first. The car may feel like it hesitates or revs up when pulling away from a stop before it grabs. Low or burnt fluid is the first thing to check. A sticking shift or pressure control solenoid, a valve body problem or a weak pump can also keep first gear from fully applying. A faulty speed sensor can create a false ratio reading too. KBB groups P0731 to P0735 together and advises avoiding driving with them. Shops check fluid, compare live input and output speeds, test line pressure and solenoid operation, and decide between a valve body repair and a rebuild.
Common symptoms
- Check engine light on
- Slipping or flare when in or shifting into first gear
- Delayed or harsh shifts
- Engine revs rise without the car speeding up
- Transmission in limp mode, stuck in one gear
Most common causes
- Low or degraded transmission fluid
- Worn first gear clutch pack or band
- Faulty shift or pressure control solenoid
- Valve body problem
- Faulty input or output speed sensor
- Weak transmission pump
What to check yourself first
Check fluid level and condition. Notice whether the car slips when pulling away from a stop, which matches a first gear fault. Avoid hard launches until it is diagnosed.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Transmission fluid change | $294-$356 | Low or burnt fluid causes many transmission codes. Check the correct fluid type for your transmission. |
| Transmission diagnosis with a full scan | $125-$183 | A transmission scan reads the codes stored in the transmission computer, which a basic reader may miss. |
| Transmission filter and fluid service | $621-$785 | Worth doing if the filter is clogged or the fluid is overdue. |
| Replace transmission (if internally damaged) | $6,238-$6,764 | If first gear clutches are worn out. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0730 Incorrect Gear Ratio
- P0732 Gear 2 Incorrect Ratio
- P0733 Gear 3 Incorrect Ratio
- P0700 Transmission Control System (MIL Request)