# P0730: Incorrect Gear 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, shift solenoid, or internal wear - **DIY?:** Check fluid only ## Quick answer P0730 means the transmission computer has compared input and output shaft speeds and found that they do not match any gear the transmission should be in. In plain terms, the transmission is slipping or not fully engaging a gear. Low or worn-out fluid, a failing shift solenoid, or worn internal parts are the usual causes. ## What does P0730 mean? An automatic transmission gets each gear by applying a specific set of clutches or bands with hydraulic pressure. Each gear has a fixed ratio between how fast the input shaft turns and how fast the output shaft turns. The transmission computer reads both speeds from sensors, or uses engine RPM on some designs, and calculates the actual ratio many times a second while you drive. P0730 sets when that calculated ratio does not match the gear the computer has commanded, beyond an allowed tolerance and for longer than a set time. That usually means a clutch or band is slipping, or a gear is not fully engaging. When the computer can tell which gear is affected, many vehicles store a gear-specific code, such as P0731 for first gear or P0732 for second, alongside or instead of P0730. ## What are the symptoms of P0730? - Engine revs rise without the car speeding up (slipping) - Harsh, delayed, or missing shifts - Transmission stuck in one gear (limp mode) - Check engine light on, often with P0700 ## What causes P0730? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Low or worn-out transmission fluid** (most common). Transmission fluid supplies the pressure that clamps the clutches together. Low fluid from a leak, or fluid broken down by heat and age, cannot hold them firmly, so they slip. Dark, burnt-smelling fluid is a warning sign. Vehicles that tow, haul, or work in heat are most affected, and some transmissions are sensitive to the wrong fluid type. 2. **Failing shift solenoid or valve body** (common). Shift and pressure control solenoids direct fluid to the right clutches through passages in the valve body. A sticky solenoid, a worn valve bore, or trapped debris can lower pressure to one clutch, causing slipping in certain gears only. Slipping that appears in one gear, or only once the transmission is hot, often points here rather than to general wear. 3. **Worn clutches or bands inside the transmission** (common). Friction clutches and bands wear with mileage, heat, and hard use, much like brake pads. Once worn, they slip no matter what the fluid looks like, and the fluid often turns dark and carries friction material. This is more likely at high mileage or after the transmission has overheated, and it usually means a rebuild or replacement. 4. **Faulty input or output speed sensor** (less common). The ratio calculation depends on accurate input and output speed signals. A failing speed sensor or a damaged sensor wire can make the computer think the transmission is slipping when it is not. Speed sensor codes such as P0715 stored alongside P0730, or a speed reading that drops out on a scan tool, point to the sensor first. 5. **Clogged transmission filter** (less common). The transmission filter screens debris out of the fluid on its way to the pump. A filter clogged with friction material or sludge starves the pump and lowers pressure, especially at higher RPM or when the fluid is cold. A clogged filter often signals internal wear, so a shop also inspects the debris in the pan when replacing it. ## How do you diagnose P0730? 1. Check fluid level and condition using your vehicle's procedure. 2. Read all transmission codes. A gear-specific code like P0731 or P0732 shows which gear is slipping. 3. Compare input and output speed readings on a scan tool while driving. 4. Have a shop test line pressure and solenoid operation before deciding on internal repair. ## How do you fix P0730, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Top up or service transmission fluid | $150-$350 | Can help if fluid was low or old and there is no internal damage. | | Replace shift solenoid or valve body | $400-$1,500 | For a confirmed solenoid or valve body problem. | | Rebuild or replace transmission | $2,800-$5,500 | Needed when clutches or bands are worn out. | ## Is it safe to drive with P0730? > **Drive to a shop this week.** Drive as little as possible. A slipping transmission can get worse quickly and can leave you without power when merging or climbing, so get it checked soon. ## Will P0730 fail an emissions test? P0730 turns on the check engine light, so the car fails an OBD-II emissions test in most states. Clearing the code will not help for long, because a slipping transmission sets it again quickly, and clearing also resets the readiness monitors. The repair has to come before the retest, and there is no cheap way around it. ## After the repair: clearing P0730 After the repair, clear transmission and engine codes and perform any adaptive relearn your transmission needs, since many modern units adjust shift timing to wear. Test drive through every gear, including uphill and under firm throttle where safe. Engine RPM should rise and fall in step with road speed, and P0730 should not return over several weeks. ## How to prevent P0730 - Change transmission fluid at the interval in your manual, and sooner if you tow or haul. - Use only the fluid type specified for your transmission, because the wrong fluid can cause slipping. - Check for red or brown spots under the car and fix transmission leaks early. - Stay within your vehicle's towing rating, since overloading overheats fluid and wears clutches fast. - Get slipping or flared shifts checked at the first sign, before the damage spreads. ## Codes often seen with P0730 - [P0700](/codes/p0700): Transmission Control System (MIL Request) - [P0715](/codes/p0715): Input/Turbine Speed Sensor "A" Circuit - [P0741](/codes/p0741): Torque Converter Clutch Solenoid Circuit Performance/Stuck Off - [P0500](/codes/p0500): Vehicle Speed Sensor "A" ## Frequently asked questions ### Can I drive with a P0730 code? Only short, gentle trips, because a slipping transmission can lose power without warning and gets worse with use. Avoid highways, steep hills, and towing, since losing drive while merging or climbing is dangerous. Have it diagnosed soon, because continued slipping can turn a solenoid repair into a full rebuild. ### Can a fluid change fix P0730? Sometimes, if fluid was low or badly worn and the transmission is not damaged. If the transmission already slips, a fluid change will not repair worn clutches. A shop can learn a lot from the fluid's color, its smell, and any debris in the pan before recommending a fluid service or a bigger repair. ### How much does it cost to fix P0730? Costs range from about $150 for a fluid service to $5,500 for a rebuild or replacement. A shift solenoid or valve body repair falls in between at roughly $400 to $1,500. Paying for a proper diagnosis, including a line pressure test, is worth it before committing to a major repair. ### What does incorrect gear ratio mean? It means the transmission's input and output shaft speeds do not match the gear it should be in. Usually the input side is spinning faster than it should, which shows a clutch or band slipping. In plain terms, the engine revs without the car gaining speed the way it normally would. ### What is the difference between P0730 and P0731? P0730 is the general incorrect gear ratio code, while P0731 through P0736 name a specific gear, such as P0731 for first gear and P0732 for second. A gear-specific code helps narrow the cause to particular clutches or solenoids. Some transmissions set only P0730, while others set both. ### Can low transmission fluid cause P0730? Yes, low fluid is one of the most common causes. Without enough fluid, the pump cannot build enough pressure to hold the clutches, so they slip, often in turns or on hills when fluid sloshes away from the pickup. Check the level using your vehicle's procedure and look for leaks. ### Can I fix P0730 myself? Checking fluid level and condition is the main DIY step, and topping up with the correct fluid is reasonable if it is low. Diagnosing solenoids, line pressure, and internal wear takes a shop with a scan tool and pressure gauges. Be wary of additives that promise to stop slipping, since they cannot restore worn parts. ### Should I rebuild or replace my transmission? It depends on the price and the damage found. A rebuild by a reputable shop keeps your original unit and can cost less, while a remanufactured unit often comes with a longer warranty. Get written quotes, compare warranty length and coverage, and weigh the total against the value of the car. ### Will P0730 fail an emissions test? Yes, in most OBD-II testing states, because P0730 turns on the check engine light. If the transmission is slipping, the code usually returns soon after being cleared, and clearing resets the readiness monitors anyway. The transmission needs to be repaired before the car can pass. ### What does a slipping transmission feel like? It feels like engine revs climbing without the car speeding up to match, as if you pressed the clutch on a manual car. It may happen during a shift, when pulling away from a stop, or while climbing a hill. You may also notice delayed engagement into gear or a burning smell. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## 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) - [P0731 Gear 1 Incorrect Ratio](https://diagxcar.com/codes/p0731) - [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) - [P0500 Vehicle Speed Sensor "A"](https://diagxcar.com/codes/p0500) - [P0841 Transmission Fluid Pressure Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0841) ## Symptoms - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) - [Why does my car jerk when I accelerate?](https://diagxcar.com/symptoms/car-jerks-when-accelerating) - [Why is my car leaking transmission fluid?](https://diagxcar.com/symptoms/car-leaking-transmission-fluid) - [Why is my transmission slipping?](https://diagxcar.com/symptoms/transmission-slipping) - [Why does my car whine when I accelerate?](https://diagxcar.com/symptoms/whining-noise-when-accelerating) ## Repair costs - [Transmission replacement cost](https://diagxcar.com/cost/transmission-replacement) --- Source page: https://diagxcar.com/codes/p0730 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.