P0731: Gear 1 Incorrect Ratio
What to do
You may feel slipping or a flare in revs when pulling away from a standstill, with the rest of the drive feeling normal. Have it looked at now rather than when it spreads — this is the point at which the cheap causes are still the likely ones.
What this code means
The measured ratio in first gear does not match what first should give. First carries more torque than any other forward gear, so a clutch that is marginal anywhere will usually reveal itself here first — which makes a fault confined to first an early warning rather than a late one.
The practical consequence is that a first-gear ratio fault caught while every other gear is still correct is the best time this problem is ever going to be found. The full diagnostic order is set out under P0730 and applies unchanged: verify the speed sensors, then fluid and pressure, then the solenoids, and only then anything internal.
Likely causes
Start here
- Low or degraded transmission fluid · easy
- Failed shift solenoid · moderate
- Low transmission line pressure · specialist
Less common
- Worn valve body · specialist
- Worn clutch packs · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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