Gear 1 Incorrect Ratio
What does P0731 mean?
The P0731 code means the vehicle's onboard diagnostic system has detected: Gear 1 Incorrect Ratio. This is a critical severity code.
Common Symptoms
- Check Engine Light illuminated
- Slipping in first gear
- No first gear engagement
- RPM flare when starting from stop
- Harsh 1-2 shift
Probable Causes (Ranked by Likelihood)
- Worn first gear clutch pack Very High
- Faulty 1-2 shift solenoid High
- Low transmission fluid pressure Moderate
- Damaged first gear band Moderate
Step-by-Step Diagnostic Procedure
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Check transmission fluid level and condition
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Monitor gear ratio in first gear -- compare input to output speed ratio against specification
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Check 1-2 shift solenoid operation with a scan tool
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Perform a line pressure test in first gear
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If internal components are worn, transmission rebuild may be required
Frequently Asked Questions
Can I drive with code P0731?
Do not drive. An incorrect gear ratio indicates the transmission is slipping or not engaging properly. Continued driving can cause catastrophic transmission failure.
Does P0731 mean I need a new transmission?
Not always, but often. If the cause is a worn clutch pack or band, a transmission rebuild or replacement is typically necessary. If a solenoid or valve body is the cause, repair may be less extensive.
How is gear ratio measured for P0731?
The TCM compares input shaft speed to output shaft speed. The calculated ratio should match the expected gear ratio. When the ratio deviates beyond a threshold, the code is set.