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DTC code page

P0731: Gear 1 Incorrect Ratio

Quick answer: The transmission controller commanded first gear, but the measured speed relationship did not match the ratio expected for first gear.

Drivers also search this fault as gear 1 incorrect ratio, first gear incorrect ratio, transmission stuck in first ratio error.

Severity: high Family: powertrain Related paths: 9
Meaning

What P0731 usually means

P0731 narrows the broad P0730 gear-ratio story down to first gear. That matters because a wrong ratio in first often shows up during launch, stop-and-go takeoff, or the first shift after selecting Drive. Sometimes the ratio is wrong because input or output speed data is false. Other times first-gear apply really is weak because of low line pressure, a leaking clutch circuit, a bad low/reverse element, or valve-body wear that prevents a clean first-gear apply.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Ask whether the vehicle slips or bangs specifically on takeoff, because that points harder at a first-gear problem than a random highway complaint.
  • Check for companion speed-sensor and shift-solenoid codes before calling it internal failure.
  • Inspect fluid condition and note whether engagement into Drive is delayed when cold or hot.
Driving risk

Can you keep driving?

A vehicle with P0731 may slip badly on takeoff or default into limp mode. Driving it regularly can accelerate clutch damage, so keep use minimal until the ratio problem is understood.

High urgency: If symptoms are active, reduce driving and diagnose quickly before secondary damage builds.
Likely causes

Common causes behind this code

  • False input or output speed data causing the TCM to miscalculate first-gear ratio
  • Low or contaminated transmission fluid reducing first-gear apply pressure
  • Valve-body wear or sticking shift valves affecting first-gear command
  • Internal first-gear clutch, band, or one-way element slip
  • Electrical solenoid or hydraulic fault that leaves the unit starting in fail-safe strategy

Cause phrases often tied to this code: low transmission fluid, bad input speed sensor, bad output speed sensor, valve body wear, first gear clutch slip.

Diagnostic order

Suggested workflow

  1. Capture freeze-frame and verify whether the fault set during launch, a coast-down reapply, or fail-safe operation.
  2. Compare input speed, output speed, and commanded gear during takeoff if live data is available.
  3. Check for speed-sensor plausibility first so a false ratio calculation does not send you straight to hard parts.
  4. If data is credible, evaluate fluid condition, line-pressure control, and valve-body behavior.
  5. If first gear still slips with believable data, move toward internal clutch, band, or one-way mechanical diagnosis.
Avoid guesswork

Common mistakes

  • Assuming any gear-ratio code is automatically a full rebuild without verifying speed data first.
  • Ignoring the launch-specific complaint and road-testing only at cruise.
  • Calling a delayed engagement problem normal wear without checking line pressure and fluid condition.
Repair path

Practical fix guidance

  • Prove whether P0731 is a false first-gear math problem or a real first-gear apply problem.
  • Repair speed-sensor, wiring, or solenoid faults first when live data points there.
  • If the ratio error is real, move quickly toward hydraulic and internal transmission inspection before more clutch material is lost.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0731

Useful when the driver knows the wording but not the exact DTC yet.

  • gear 1 incorrect ratio
  • first gear incorrect ratio
  • transmission stuck in first ratio error
Related search intent

Queries this page can answer naturally

  • P0731 code meaning
  • what does P0731 mean
  • gear 1 incorrect ratio symptoms
  • first gear slipping transmission
FAQ

Quick questions about P0731

Does P0731 mean first gear is slipping?

Often yes, but not always. Bad speed data can create a false first-gear ratio story, so the sensor inputs still need to be checked.

Why does P0731 feel worst from a stop?

Because the fault is tied to first gear, which is most heavily used during launch and low-speed takeoff.

Can low fluid trigger P0731?

Yes. Low or degraded fluid can weaken first-gear apply enough to create a ratio error.