Parts
$50-3000+
P0731 — Gear 1 Incorrect Ratio
CAUTIONIs it safe to drive? The transmission is slipping or not engaging 1st gear correctly. Drive gently — continued slipping damages clutch packs.
What P0731 means
The TCM measured the input-to-output ratio in 1st gear and it didn't match spec. Could be a mechanical slip in 1st-gear clutches, a solenoid, or dirty fluid. Exact behavior and repair depth varies by make.
Most likely causes (in order)
- Low or burnt transmission fluid
- Worn 1st-gear clutch pack
- Shift solenoid for 1st gear
- Speed sensor error (false ratio reading)
- Valve body or pressure issue
Symptoms you might notice
- Slipping in 1st gear
- Hard engagement from stop
- Trans light / limp mode
What to check first
Fluid level and condition first. If slipping is felt, read live data — compare input vs. output speed in 1st. Internal work requires a shop with brand-specific rebuild data.
Repair cost & difficulty
Labor
3-20+ hr
Difficulty
Shop job