P0731 — Gear 1 Incorrect Ratio
P0731 is the standardized powertrain DTC for “Gear 1 Incorrect Ratio.” The code identifies the monitored condition; it does not by itself prove which part failed.
What P0731 means
P0731 is the standardized powertrain DTC for “Gear 1 Incorrect Ratio.” The code identifies the monitored condition; it does not by itself prove which part failed.
How to interpret the code wording
“Incorrect Ratio” means input and output speed do not match the ratio expected for the commanded gear or direction. Confirm fluid level/condition, commanded gear, speed-sensor data, hydraulic pressure/control, clutch/band operation, and internal mechanical condition using transmission-specific service information.
Possible symptoms
- Slipping or flare between shifts
- Limp mode
- Harsh or delayed engagement
- Abnormal RPM for vehicle speed
- Transmission warning
Causes to test
These are diagnostic possibilities, not a statistical parts-replacement ranking. Vehicle-specific service information takes priority.
- Low or incorrect transmission fluid
- Hydraulic pressure/control problem
- Valve body or solenoid fault
- Speed-sensor data error
- Internal clutch, belt, pulley, or mechanical damage
Step-by-step diagnostic workflow
- Check fluid level/condition exactly as specified for the transmission.
- Scan the TCM for companion codes; a P0700 in the ECM is not the root cause.
- Compare commanded gear with input/output speed and calculated ratio.
- Diagnose pressure/solenoid/speed-sensor codes before concluding internal failure.
- Follow OEM transmission-specific pressure and mechanical inspection procedures.
- Clear codes only after repair, then complete an appropriate drive cycle and verify the code and symptoms do not return.
Scan data worth checking
- Commanded and actual gear
- Input/turbine speed
- Output speed
- Transmission fluid temperature
- Line pressure or pressure-control command where supported
Severity and drivability
High enough to avoid heavy use until diagnosed. Incorrect-ratio/slip codes can indicate hydraulic pressure loss or internal clutch/belt damage.
Stop driving and investigate immediately if there is a flashing MIL, oil-pressure warning, overheating, fuel leakage, severe misfire, major loss of power, abnormal mechanical noise, or a transmission that is slipping badly.
Common diagnostic mistakes
- Treating P0700 as the actual transmission failure
- Adding fluid without using the correct level procedure
- Assuming an incorrect-ratio code always means a complete transmission replacement
Related generic codes
Source and accuracy notes
Generic DTC structure and standardized definitions are governed by SAE J2012/J2012DA. Actual enable criteria, thresholds, circuit pinouts, test values, software conditions, and repair procedures vary by vehicle. Use current OEM service information for the exact year/engine/calibration and check applicable manufacturer technical service bulletins. See the site methodology and primary-reference policy.