P0731 Code: Gear 1 Incorrect Ratio
While in first gear, the transmission's input and output speeds don't match the first-gear ratio.
At a glance
Severity: Moderate
- Meaning
- Gear 1 Incorrect Ratio
- System
- Transmission · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $120–$6,500
- DIY difficulty
- Hard
First gear has the steepest ratio in the transmission, typically around 3 to 4.7:1, so the TCM expects the input shaft to spin that many times faster than the output shaft. If the measured ratio stays off while 1st is commanded, P0731 is stored. In many planetary automatics, 1st gear in Drive is held by a one-way clutch (a roller or sprag clutch) together with the forward or underdrive clutch; in Honda-style parallel-shaft units it is the 1st clutch plus a one-way clutch. Because first gear carries the highest torque, a worn holding device shows up here first, usually as a flare when pulling away. A weak output speed signal at crawling speed can also fake this code.
Can I keep driving? Pull away gently and avoid steep hills, towing and full throttle from a stop. Once moving, the transmission may feel normal in higher gears, but every slipping launch heats and wears the parts further.
How to read P0731
- P Powertrain
- 0 Generic (SAE)
- 7 Transmission
- 31 Specific fault
Symptoms
- Engine revs up when pulling away from a stop before the car starts moving
- Sluggish launch that suddenly catches with a thump
- Normal driving once it has shifted into 2nd
- Slip is worse uphill, with passengers or with a trailer
- Delayed engagement when moving the lever into Drive
- Check engine light, sometimes with P0700
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Worn or slipping one-way clutch (roller or sprag) that holds 1st in Drive
- Low fluid or a clogged filter starving the pump at launch
- Worn forward or underdrive clutch pack
- Output speed sensor signal dropping out at very low speed
- Worn low/reverse clutch or, on Honda units, the 1st clutch
- Pressure regulator or accumulator problem softening the 1st-gear apply
- Incorrect adaptive values after battery disconnection or a fluid change
Diagnosis step by step
Check which gears are affected
Read the TCM codes and look for other ratio codes. P0731 alone points to parts that only work in 1st; P0731 together with P0732 and P0733 points to a clutch shared by the lower gears, such as the forward or underdrive clutch.
Tools: OBD-II scanner
Check fluid level and smell
Check the fluid level at the correct temperature and look for a burnt smell. A level that is only slightly low can uncover the pickup when the car launches or sits on an incline, which causes slip in 1st before anything else.
Tools: Flashlight, Towels & shallow pan
Compare Drive with manual Low
Pull away gently in Drive, then again with the selector in 1 or L. On many units, manual low applies an extra clutch or band that also holds 1st. If the slip disappears in manual low, the one-way clutch is the prime suspect.
Tools: OBD-II scanner
Watch output speed at crawling speed
Graph output shaft speed while rolling off from a stop. It should rise smoothly from zero; a signal that stays at zero until 5–8 mph, or flickers, suggests a weak sensor, a wide air gap or metal debris on the sensor tip.
Tools: OBD-II scanner, Multimeter
Shop stall test
A technician may run a short stall test, holding the brakes at full throttle for no more than a few seconds, and compare engine rpm with the specification. Stall speed that is too high in Drive but normal in Reverse points to the forward-gear holding devices.
Inspect pan and filter
Remove the pan and check the filter and magnet. Metal needles or flakes from a roller clutch, or dark friction material, confirm internal wear.
Tools: Towels & shallow pan, Torque wrench
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Fluid and filter service | No | $150–$400 |
| Clean or replace output speed sensor | No | $120–$400 |
| Transmission overhaul including one-way clutch and forward clutch | No | $2,500–$5,000 |
| Remanufactured transmission, installed | No | $3,200–$6,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Chevrolet
In the GM 4L60E and 4L65E used in Silverado, Tahoe and similar trucks, 1st gear in Drive relies on the low roller clutch. A worn roller clutch slips on takeoff in Drive but usually holds in manual 1, because the low/reverse clutch then applies as well.
Field data
| Ford | 18 | F-150 SUPERCAB, F-150 SUPER CREW, Escape | |
|---|---|---|---|
| Chrysler | 2 | Town And Country | |
| Dodge | 2 | Journey, RAM 2500 |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
Emission test stations fail a vehicle with the check engine light on, and P0731 turns it on. Clear the code only after the repair, then drive until readiness monitors are complete.
Frequently asked questions
Why does my car slip only when starting from a stop?
First gear multiplies engine torque the most, so a worn holding device is overwhelmed there first. Once the transmission shifts to 2nd, other clutches take over and the car can feel normal.
Can a bad speed sensor cause P0731?
Yes. Output speed sensors produce a weak signal at very low speed, and debris on the magnetic tip or a wide air gap can make the TCM think 1st gear is slipping when it isn't.
Does P0731 mean I need a new transmission?
Not always, but if slip is confirmed and the fluid level is right, the holding parts are inside the transmission and repair usually means an overhaul. Rule out fluid level and the speed sensor before paying for it.