P0731: Gear 1 Incorrect Ratio
Updated November 15, 2026
The transmission computer compares input and output speeds to confirm the transmission is really in the gear it commanded. P0731 means the ratio in first gear doesn't match, which usually means the transmission is slipping in first or not fully engaging it.
COMPZA may earn a commission when you buy through links on this page, at no extra cost to you. How we make money.
🔧 Want to check this yourself? An OBD2 scanner reads the code; models with live data also show the sensor readings used in the checks below. See code readers and scanners from $24.99 ↓ · Which scanner do I need?
Common causes
- Low, burnt or degraded transmission fluid
- Worn clutches or bands that apply first gear
- A faulty shift solenoid or pressure control solenoid, or a valve body problem
- A clogged transmission filter
- A faulty input or output speed sensor giving a false reading
Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.
Symptoms
- Engine RPM flaring when pulling away without the car speeding up
- Slow or delayed engagement into drive
- Harsh or late shift from first to second
- Transmission stuck in one gear (limp mode)
- Check engine or transmission warning light
Is it safe to drive?
If the transmission is slipping, won't move properly or is stuck in one gear, stop driving and have it towed; continued slipping can destroy the transmission. If it drives normally with a steady light, check the fluid right away, drive gently and get it diagnosed soon.
How to check it with a scanner
- Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
- Check the transmission fluid level and condition using your vehicle's procedure; many must be checked warm with the engine running, and some sealed units need a shop. Keep hands clear of belts and the fan. Very dark or burnt-smelling fluid is a warning sign.
- Scan the transmission module for other ratio, solenoid or speed sensor codes; they narrow down the cause.
- If your scanner shows them, have a passenger compare input and output shaft speeds in live data while pulling away in first gear.
- Use only the transmission fluid type your vehicle specifies.
- After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.
A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.
Code readers and scanners in stock
From partner stores' live product feeds. Check that the tool covers your vehicle's make, model and year on the retailer's page before you buy.
LAUNCH CR319 OBD2 Code Reader & Emissions Readiness Tester$24.99at LAUNCH X431 Online 
LAUNCH CR529 OBD2 Code Reader with Live Data Stream$45at LAUNCH X431 Online 
Autel MaxiLink ML529$52at AUTELOnline 
AutoLink AL319$59at AUTELOnline 
MaxiAP AP2500E$60at AUTELOnline 
LAUNCH Creader VII+ Code Reader for Engine, ABS, SRS & Transmission$119at LAUNCH X431 Online Affiliate links. AUTELOnline prices updated Nov 15, 5:03 AM EST · LAUNCH X431 Online prices updated Nov 15, 4:03 AM EST.
Some transmissions need an adaptive relearn with a scan tool after fluid service or solenoid replacement; check your service information.
Search eBay for your vehicle
Affiliate links: COMPZA may earn a commission from qualifying eBay purchases at no extra cost to you. Add your vehicle in eBay's parts finder to see parts that fit.
Questions
What does P0731 mean?
P0731 is the generic OBD2 code for "Gear 1 Incorrect Ratio." The transmission computer compares input and output speeds to confirm the transmission is really in the gear it commanded. P0731 means the ratio in first gear doesn't match, which usually means the transmission is slipping in first or not fully engaging it.
Is it safe to drive with P0731?
If the transmission is slipping, won't move properly or is stuck in one gear, stop driving and have it towed; continued slipping can destroy the transmission. If it drives normally with a steady light, check the fluid right away, drive gently and get it diagnosed soon.
How do I check P0731 myself?
Read the code and freeze-frame data with an OBD2 scanner, then: Check the transmission fluid level and condition using your vehicle's procedure; many must be checked warm with the engine running, and some sealed units need a shop. Keep hands clear of belts and the fan. Very dark or burnt-smelling fluid is a warning sign. Scan the transmission module for other ratio, solenoid or speed sensor codes; they narrow down the cause. If your scanner shows them, have a passenger compare input and output shaft speeds in live data while pulling away in first gear. Use only the transmission fluid type your vehicle specifies.
Related codes
📬 Get the weekly deals email
One email a week with the best current deals from our partner stores: home, kitchen, tech, car and gifts. No spam, unsubscribe anytime.
Emails include affiliate links; COMPZA may earn a commission at no extra cost to you. See our privacy policy.