P0730
- Powertrain
- Generic (SAE)
Get it looked at now
A transmission that cannot hold its commanded ratio is either slipping, which destroys friction material and overheats fluid with every mile, or engaging the wrong gear, which produces unpredictable acceleration and engine speed. Failsafe mode locked in one gear also limits your ability to accelerate away from a hazard.
- Safe to drive
- Drive as little as possible. Slipping builds heat that worsens the damage. If it flares, slips or bangs into gear, arrange a tow.
Incorrect Gear Ratio
The transmission control module compared how fast the input shaft is turning against how fast the output shaft is turning, and the resulting ratio does not match what the module expected for the gear it commanded. That means either the transmission is slipping, or it is actually in a different gear than the one requested — the code does not tell you which.
The module continuously computes actual ratio as input speed divided by output speed and compares it to the calibrated ratio for the commanded gear. Both of those speeds are normally measured inside the transmission, ahead of the final drive. P0730 is the general-purpose version of this test: it sets when the mismatch cannot be attributed to one specific gear, or when the fault appears across several gears. The gear-specific relatives P0731 through P0736 set when the mismatch is repeatable in one gear only.
How the car detected itWith the transmission in a commanded gear and driveline load steady, the module samples both speed sensors and calculates the ratio. If the calculated ratio falls outside the tolerance band for that gear for a calibrated time — and the enabling conditions are met, typically stable throttle, adequate fluid temperature and no speed sensor faults stored — it sets the code. Many calibrations require the failure on two consecutive drive cycles before commanding the light and dropping to failsafe.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Drive as little as possible. Slipping builds heat that worsens the damage. If it flares, slips or bangs into gear, arrange a tow.
- Urgency
- Get it looked at now
- Will it pass emissions
- Not affected
- If ignored
- If the cause is slipping, continued driving shreds clutch friction material into the fluid, which circulates through the valve body and plugs passages — turning a solenoid or valve body repair into a full rebuild. If the cause is a wrong-gear engagement, the shock loading damages planetary components and one-way clutches.
- Check engine light
- Solid
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Internal slippage | Very common | — |
| 2 | Valve body fault | Common | — |
| 3 | Speed sensor reading inaccurate | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Fluid level, color, smell and the condition of the pan magnet
Low or burnt fluid causes exactly this symptom and costs nothing to check. A pan magnet packed with friction material or metal answers the mechanical-versus-electrical question straight away.
Whether the failed ratio matches a different gear exactly, or drifts
Read this before anything else, because it splits the diagnosis in two. A ratio that lands precisely on another gear's value means the transmission engaged the wrong gear — look at solenoids and the valve body. A ratio that wanders under load means slipping — look at pressure and friction elements.
Which speed source the module uses for output speed
Most transmissions measure output shaft speed inside the case, ahead of the final drive, so tire size and differential ratio cannot affect the ratio calculation. On the minority of applications where the module derives output speed from a vehicle speed sensor downstream of the transmission or from ABS wheel speed over the bus, a rolling-radius or final-drive change can shift it. Check the wiring diagram to see which source the module uses before pursuing this.
Companion codes, especially speed sensor and solenoid codes
A stored input or output speed sensor code makes the ratio calculation itself unreliable. Fix the sensor fault first, then re-evaluate — the ratio code may not return.
Manufacturer service bulletins for the exact transmission
Several transmissions have known valve body wear points or calibration updates covered by bulletins. Checking first can save hours of testing.
Verify fluid condition and level to the manufacturer's procedure
Tools Manufacturer service procedure, scan tool for fluid temperature
Level checking varies widely — some transmissions use a dipstick hot and running, others a fill plug at a specified fluid temperature, and many have no dipstick at all. Follow the correct procedure for the vehicle. Note color and smell, and inspect the pan magnet and filter if the pan is already off.
ExpectedCorrect level at the specified temperature, fluid still red or amber rather than dark brown, no burnt smell, no friction material on the magnet
Capture freeze frame and reproduce the fault on a road test
Tools Bidirectional scan tool with graphing, safe road-test route
Note the gear, speed, throttle position and fluid temperature stored in freeze frame. Then road test with input speed, output speed, commanded gear, actual gear and calculated ratio all on screen, and reproduce the conditions.
ExpectedYou can see the exact moment ratio departs from the commanded gear, and in which gear or gears it happens
Decide between wrong gear and slipping
Tools Scan tool data, transmission gear ratio specification
Compare the failing ratio to the published ratio table for this transmission. If the measured ratio equals another gear's ratio, the transmission engaged the wrong gear and the fault is hydraulic or electrical. If the ratio sits between gears or moves around under load, it is slipping and the fault is pressure or friction material.
ExpectedA clear answer to which of the two failure modes you are dealing with
Measure line pressure with a mechanical gauge
Tools Transmission pressure gauge set, factory pressure chart
Connect a gauge at the line pressure test port where one exists and compare against the manufacturer's pressure chart at idle, in each range, and under load. Pressure specifications are entirely vehicle-specific. Where no test port exists, use the module's pressure sensor data as a secondary reference and note that it is less trustworthy.
ExpectedPressure within the published range at each test condition, and pressure that rises appropriately with throttle
Test the shift solenoids electrically and functionally
Tools DMM, bidirectional scan tool, wiring diagram, vehicle lift or stationary test conditions
Measure resistance on each solenoid and check for shorts to ground and to each other. Then use the scan tool's bidirectional control to command each solenoid individually and confirm the transmission responds with the expected ratio change. Perform bidirectional solenoid commands with the vehicle stationary, or with the drive wheels supported on a lift, following the manufacturer's procedure — never while driving on public roads, because commanding a solenoid at speed can force an abrupt gear change or a neutral condition. A solenoid that passes resistance but does not move fluid is a common failure.
ExpectedResistance within spec for each solenoid, and a matching ratio change when each is commanded
Verify speed sensor accuracy against an independent reference
Tools Scan tool with ABS data access, GPS reference, wiring diagram for the specific vehicle
Compare output shaft speed against actual road speed measured another way — GPS speed, or a wheel speed sensor from the ABS module. Before treating a mismatch as a calibration problem, check the wiring diagram to see where output speed actually comes from. If it is measured inside the case, tire size and final drive ratio are irrelevant to the ratio calculation. Only where the module derives output speed from a vehicle speed sensor downstream of the transmission or from ABS wheel speed does the tire size and final drive need to match what the module is calibrated for.
ExpectedOutput speed converts to a road speed within a few percent of the independent reference
Inspect the valve body and separator plate if hydraulics are implicated
Tools Hand tools, clean workspace, valve body inspection references
With the pan down, inspect for a cracked or eroded separator plate, blown gaskets, worn valve bores and a clogged filter. Check bore wear on the pressure regulator and shift valves by feel — sticky or loose valves cause exactly this fault.
ExpectedValves that slide freely under their own weight, an intact separator plate and gaskets, a clean filter
Search bulletins and check calibration level before major work
Tools Manufacturer bulletin database, factory scan tool for calibration verification
Confirm the module is at the latest calibration and check for bulletins covering this code on this transmission. Some manufacturers address ratio faults with a software update or a revised valve body part number.
ExpectedEither a matching bulletin with a defined repair, or confirmation that no software remedy exists
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Fluid and filter service with the exact specified fluid | Fluid is low, burnt or the wrong specification, and correct ratio returns after service with line pressure back in range | $130–$400 | DIY |
| Correct the speed calibration on a vehicle whose module derives output speed from wheel or vehicle speed, after a tire or final-drive change | The wiring diagram confirms the output speed reference is downstream of the transmission, and that reference disagrees with a GPS road speed by an amount matching the changed component | $100–$300 | DIY |
| Replace a faulty shift or pressure control solenoid or solenoid pack | A solenoid fails its resistance test, or fails to produce the expected ratio change when commanded individually with the scan tool | $250–$900 | Hard |
| Rebuild or replace the valve body, including separator plate and gaskets | Line pressure out of specification with electrically sound solenoids, or inspection reveals sticking valves, worn bores or a cracked separator plate | $600–$1,800 | Shop |
| Reflash the transmission control module to the current calibration | A manufacturer bulletin covers this code on this transmission and no mechanical or hydraulic fault is found during testing | $100–$300 | Shop |
| Overhaul or replace the transmission | Ratio drifts under load with line pressure confirmed in specification and solenoids working, and the pan contains friction material | $2,500–$8,000 | Shop |
US independent shop estimates, parts plus labor, in whole dollars. The spread here is genuinely enormous because the same code covers a fluid service and a full overhaul. Insist on pressure and solenoid testing results before authorizing any repair above the valve body level. The speed calibration line is $0 only if you simply refit the original tire size yourself; any shop recalibration carries at least a half-hour of scan-tool labor. On the overhaul line, the low end reflects a common rear-drive 4- or 6-speed with a remanufactured unit available; 8- and 10-speed automatics, CVTs and transverse units with heavy removal labor routinely land above $6,500. Remanufactured unit prices also vary widely by transmission family.
- Jumping straight to a rebuild quote. Low fluid, a failed solenoid or a cracked separator plate produce this code and cost a fraction of an overhaul.
- Skipping the wrong-gear versus slipping question, which is the fork that determines everything downstream.
- Writing the code off as a tire or differential change. On most transmissions both speed sensors sit inside the case, ahead of the final drive, so a rolling-radius or final-drive change cannot move the ratio the module is testing. Confirm from the wiring diagram that output speed is actually derived from wheel or vehicle speed before pursuing this — otherwise a genuinely slipping transmission gets dismissed as a calibration issue.
- Trusting the module's internal pressure reading instead of a mechanical gauge when a test port is available.
- Replacing speed sensors because a ratio code mentions ratio. The sensors may be reporting the mechanical problem accurately.
- Using the wrong fluid specification during a service. Modern transmissions are extremely sensitive to friction modifier chemistry, and the wrong fluid can create shift faults on its own.
- Automatic Transmission
- Valve Body
- Speed Sensor
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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