# P0731: Gear 1 Incorrect Ratio **Verdict:** Drive to a shop this week Transmission - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $150-$5,500 - **Urgency:** This week - **Most likely:** Low fluid, solenoid, or worn clutches - **DIY?:** Check fluid only ## Quick answer P0731 means the transmission computer saw that the speed coming out of the transmission did not match the speed going in for first gear. In plain terms, first gear is slipping or not fully engaging. Low or worn fluid, a shift solenoid or pressure problem, or worn clutches inside the transmission are the usual causes. ## What does P0731 mean? Each gear in an automatic transmission has a fixed ratio between input shaft speed and output shaft speed. In first gear, the input shaft turns several times for each turn of the output, which gives the strong pull needed to start from a stop. The transmission computer knows that ratio and checks it constantly using the input and output speed sensors, or on some designs engine speed. P0731 sets when the measured ratio in first gear falls outside the allowed range for longer than a set time, while no speed sensor fault is present. That usually means the clutches, band, or one-way clutch that hold first gear are slipping, or the pressure applying them is too low. Which parts hold first depends on the transmission design. Because first gear carries the most torque, a slip often shows up as a flare when pulling away. Many transmissions also set P0730, and some enter limp mode. ## What are the symptoms of P0731? - Engine revs up but the car is slow to move from a stop - Delayed or harsh engagement when shifting into Drive - Transmission starts in second or stays in one gear (limp mode) - Dark or burnt-smelling transmission fluid - Check engine light, sometimes a transmission warning ## What causes P0731? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Low, burnt, or wrong fluid** (most common). First gear needs the most clamping force, so it is often the first to slip when fluid is low or worn out. A small leak at a pan gasket, cooler line, or axle seal can drop the level enough to slip on hard starts. Check the level by the maker's procedure, since many sealed units need a set fluid temperature. 2. **Worn first-gear clutches or one-way clutch** (common). The friction clutches, band, or one-way clutch that hold first gear wear with mileage, heavy loads, towing, and hard launches. Once worn, they slip under load even with good fluid. Dark fluid carrying friction material, or metal in the pan, supports this cause. Repair means removing the transmission for a rebuild or replacing it. 3. **Shift or pressure control solenoid fault** (common). Solenoids control which clutches apply and how much pressure reaches them. A sticking or weak solenoid, often caused by debris or worn fluid, can leave first gear under-pressured so it slips, especially at light throttle or when cold. Electrical solenoid codes may appear with P0731, and a scan tool command test helps confirm it. 4. **Valve body wear or internal leak** (less common). Worn valve bores, a warped separator plate, or a leaking clutch piston seal let pressure bleed off before it clamps the first-gear clutch. These leaks often worsen when the fluid is hot. Shops find them with a line pressure gauge test or by inspecting the valve body, and some transmission designs have well-known wear points. 5. **Speed sensor or software issue** (rare). If one speed sensor gives a slightly wrong reading, the computer can calculate a bad ratio even though nothing slips, although that usually sets a sensor code too. Some makers have released software updates for incorrect ratio codes on specific models. Comparing sensor data with how the car actually drives sorts this out. ## How do you diagnose P0731? 1. Check fluid level and condition using the maker's procedure, and look for leaks. 2. Read all transmission codes, including solenoid and speed sensor codes, and note the freeze-frame conditions. 3. On a scan tool, compare input and output speed in first gear during a gentle and a firmer launch. 4. Compare first gear in Drive with manual low; slipping only in Drive points to a one-way clutch on many designs. 5. Run solenoid tests and a line pressure test before deciding on internal repair. ## How do you fix P0731, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Fluid service or top-up with leak repair | $150-$450 | Can help if the fluid was low or old and the clutches are healthy. | | Replace shift or pressure control solenoid | $300-$900 | Depends on whether the solenoid is separate or part of a pack. | | Valve body repair or replacement | $600-$1,500 | When pressure testing points to valve wear or leakage. | | Rebuild or replace transmission | $2,800-$5,500 | Only when internal wear is confirmed. | Full price breakdowns: [transmission fluid change cost](/cost/transmission-fluid-change), [transmission replacement cost](/cost/transmission-replacement). ## Is it safe to drive with P0731? > **Drive to a shop this week.** Drive as little as possible, and gently. A slipping first gear can leave you unable to pull into traffic or climb a hill, and every slip burns clutch material and heats the fluid. ## Will P0731 fail an emissions test? P0731 turns on the check engine light, so it fails an OBD-II emissions test in most states. Transmission slip raises engine load and emissions, which is why it is monitored. Clearing the code resets the readiness monitors, and a real slip usually brings it back within a few drives, so repair it before testing. ## After the repair: clearing P0731 After the repair, clear codes in both computers and reset or relearn the transmission's adaptive values if your vehicle requires it. Then make several gentle and firm starts from a stop. On a scan tool, the first-gear ratio should hold steady with no engine flare. No returning code over a week of mixed driving means the fix worked. ## How to prevent P0731 - Change transmission fluid on the schedule for your use, sooner if you tow often. - Avoid hard launches and holding the car on a hill with the throttle. - Come to a complete stop before shifting between Reverse and Drive. - Fix even small transmission fluid leaks before the level drops enough to slip. - Use only the exact fluid specification listed in your owner's manual. ## Codes often seen with P0731 - [P0730](/codes/p0730): Incorrect Gear Ratio - [P0732](/codes/p0732): Gear 2 Incorrect Ratio - [P0750](/codes/p0750): Shift Solenoid "A" - [P0700](/codes/p0700): Transmission Control System (MIL Request) - [P0715](/codes/p0715): Input/Turbine Speed Sensor "A" Circuit ## Frequently asked questions ### Can I drive with a P0731 code? Only gently, and only for short trips to a shop. A slipping first gear means clutches inside are wearing every time you pull away, and the transmission heats up quickly. If the engine revs without the car moving properly, or the car will not move from a stop, have it towed. ### What does gear 1 incorrect ratio mean? It means the transmission computer measured input and output shaft speeds in first gear and found they did not match first gear's fixed ratio. In practice, first gear is slipping or not fully engaging. The computer stores P0731 when the mismatch lasts longer than it allows. ### What is the difference between P0730 and P0731? P0730 is the general incorrect gear ratio code, while P0731 says the problem is specifically in first gear. That narrows the search to the clutches, band, or one-way clutch that hold first and the solenoids that apply them. Some transmissions set both codes for the same slip. ### How much does it cost to fix P0731? Most P0731 repairs cost $150 to $5,500 at an independent shop. A fluid service with leak repair runs about $150 to $450, a solenoid $300 to $900, and valve body work $600 to $1,500. A rebuild or replacement costs $2,800 to $5,500 when internal wear is confirmed. ### Can a fluid change fix P0731? Sometimes, if the fluid was low, old, or the wrong type and the clutches are not badly worn. A fluid service is a reasonable first step on a car that slips only slightly. If the fluid is very dark or full of debris, a change alone is unlikely to fix it. ### Why does my car rev but not move from a stop? When the engine revs but the car creeps, first gear is slipping, which is exactly what P0731 describes. Low fluid, low pressure from a solenoid or valve body, or worn first-gear clutches are typical causes. Stop driving and check the fluid, because continued slipping quickly destroys clutches. ### Does P0731 mean I need a new transmission? Not always. Low fluid, a solenoid, or a valve body problem can cause P0731 and cost far less than a rebuild. A shop should check the fluid, run solenoid and pressure tests, and look in the pan for debris before recommending replacement. Ask how they confirmed internal wear. ### Can a bad speed sensor cause P0731? It can, though less often. The ratio is calculated from speed sensors, so a sensor giving a wrong reading can make first gear look like it slips. That usually also sets a sensor code such as P0715 or P0720. If the car pulls normally from a stop, test the sensors first. ### Can I fix P0731 myself? You can check and top up the fluid on vehicles with a dipstick, look for leaks, and read codes with a transmission-capable scan tool. Solenoid and valve body work need clean conditions and the right fluid-fill procedure. Clutch wear means a rebuild, which is a shop or specialist job. ### Will P0731 go away on its own? It may stop showing for a while if the slip only happens under certain loads or temperatures, but the cause usually remains. Slipping tends to get worse, not better. If the code returns or you feel flares from a stop, have the transmission checked before the damage spreads. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other transmission codes - [P0700 Transmission Control System (MIL Request)](https://diagxcar.com/codes/p0700) - [P0705 Transmission Range Sensor "A" Circuit (PRNDL Input)](https://diagxcar.com/codes/p0705) - [P0715 Input/Turbine Speed Sensor "A" Circuit](https://diagxcar.com/codes/p0715) - [P0717 Input/Turbine Speed Sensor "A" Circuit No Signal](https://diagxcar.com/codes/p0717) - [P0720 Output Shaft Speed Sensor "A" Circuit](https://diagxcar.com/codes/p0720) - [P0730 Incorrect Gear Ratio](https://diagxcar.com/codes/p0730) - [P0732 Gear 2 Incorrect Ratio](https://diagxcar.com/codes/p0732) - [P0740 Torque Converter Clutch Solenoid Circuit/Open](https://diagxcar.com/codes/p0740) - [P0741 Torque Converter Clutch Solenoid Circuit Performance/Stuck Off](https://diagxcar.com/codes/p0741) - [P0750 Shift Solenoid "A"](https://diagxcar.com/codes/p0750) - [P0841 Transmission Fluid Pressure Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0841) ## Symptoms - [Why is my transmission slipping?](https://diagxcar.com/symptoms/transmission-slipping) - [Why won't my car go into gear?](https://diagxcar.com/symptoms/car-wont-go-into-gear) - [Why is my car leaking transmission fluid?](https://diagxcar.com/symptoms/car-leaking-transmission-fluid) ## Repair costs - [Transmission fluid change cost](https://diagxcar.com/cost/transmission-fluid-change): $120-$350 - [Transmission replacement cost](https://diagxcar.com/cost/transmission-replacement): $2,500-$7,000 --- Source page: https://diagxcar.com/codes/p0731 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.