P0731 code: Gear 1 Incorrect Ratio
P0731 means gear 1 Incorrect Ratio. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0731 means
P0731 is a targeted version of the incorrect-ratio family: the computer commanded first gear, compared input and output shaft speeds, and found the ratio wrong — first gear is slipping or not engaging. A per-gear code is a diagnostic gift, because it points at the specific components that create that gear: first's clutch pack or one-way clutch, and the solenoid and valve-body circuit that apply it. Since first gear is how you leave every stoplight, symptoms cluster at takeoff — the engine revs while the car creeps, or the transmission seems to start in a higher gear. Before assuming worn clutches, the cheap causes get checked: fluid level and condition (low pressure makes any clutch slip), then the solenoid and valve body feeding first gear.
P0731 symptoms
- Engine revs high from a stop with weak acceleration
- Feels like starting out in second gear
- Slipping or shudder at low speed
- Limp mode
- Check-engine light
What it costs to fix P0731
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P0731 for my vehicle →How to fix P0731
Advanced — usually a shop job unless you’re well equipped
- Clear up speed-sensor codes before blaming first gear
The module calculates first-gear ratio from the input and output speed sensors, and a magnetic sensor makes its weakest signal at low shaft speed — exactly when first gear is engaged. Any speed-sensor code in the P0715 to P0722 range, or a speed reading that drops out at takeoff, must be fixed first, because a faulty sensor can fake a slipping first gear perfectly.
- Check the fluid for low level and burnt smell
Low fluid lets the pump suck air when the car leans or brakes hard, so first-gear slip that comes and goes after turns or stops is a classic low-level sign. Check the level using your transmission's procedure and note the smell — a burnt odor means clutches have already been overheating.
- Compare Drive with manual low
On many automatics, first gear in Drive relies on a one-way clutch, while selecting manual low applies an extra clutch or band to hold the same gear. If the car slips in Drive but pulls cleanly in manual low, the one-way clutch is the prime suspect; slip in both points at the shared clutch pack or low apply pressure.
- Command the shift solenoids for first gear
Look up which solenoids are on and off in first in your unit's shift chart, then use a bidirectional scan tool to command each one and listen for a click while checking its circuit resistance against spec. A solenoid that doesn't respond, or reads out of range, is a far smaller repair than a clutch pack.
- Plan for internal repair if the mechanical side is gone
When fluid, sensors, and solenoids check out, the fault is a worn first-gear clutch, a failed one-way clutch, or a leaking seal in that circuit, all of which mean removing and disassembling the transmission. Get a written diagnosis, and expect adaptive relearning after the rebuild so the new clutches apply smoothly.
DIY or shop? Fixing a speed-sensor fault, checking the fluid, and the Drive-versus-low comparison are things an owner can do, and they decide whether this is a minor fix or a teardown. Solenoid testing needs a bidirectional scan tool, and a pan-mounted solenoid can be a DIY job on some units. Internal clutch or one-way clutch failure means pulling the transmission, which is shop or specialist work. Limit driving meanwhile: first gear slips on every takeoff, so heat damage builds fast.
Tools for the DIY steps: Bidirectional scan tool · Digital multimeter · Transmission fluid of the specified type · Drain pan · Service manual shift-solenoid chart
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0731.
Start a case with P0731 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0731?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0731: common questions
Why does a per-gear code matter?
Because each forward gear is created by its own combination of clutches and solenoid commands. P0731 says the failure lives in first gear's specific hardware — its clutch pack, one-way clutch, or apply circuit — which narrows the hunt dramatically compared to a general slip code.
Is it the solenoid or the clutch pack?
That's the pivotal question, and pressure testing usually answers it. A sticking solenoid or valve body fails to deliver pressure (cheaper fix); a worn clutch pack slips even with good pressure (internal repair). Fluid full of friction material tips the scales toward the clutch.
Can I drive with P0731?
Redline can't make that call from the code alone. Every launch from a stop slips and heats the exact clutch that's failing, so the damage grows with each start. Get it diagnosed promptly, and if it flares badly from stops, stop driving and tow it.
Would a fluid change fix this?
Sometimes — if the root cause is low level or degraded fluid sticking a valve, fresh fluid and a filter can genuinely resolve it. But if the pan shows heavy clutch material, the fluid was the symptom, not the cause, and expectations should adjust accordingly.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0731 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0731 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.