Symptom
Transmission stuck in one gear
The automatic transmission no longer changes gear — typically holding third or fourth, with strained acceleration from rest and low engine speed on the motorway. This is almost always the transmission protecting itself rather than a mechanical breakdown: having lost a signal it depends on, the module selects one gear it can guarantee and stops shifting. It is designed to get the vehicle home, not to be driven on, because the torque converter stays unlocked in that state and puts heat into the fluid that the cooler was never sized to remove.
Also described as: stuck in gear, won't change gear, limp mode transmission, stuck in third, no gear changes, gearbox limp mode, one gear only, won't shift, transmission limp mode, گیربکس روی یک دنده گیر کرده, دنده عوض نمیشود, atascada en segunda, queda misma marcha, caja bloqueada marcha, الجير عالق على غيار واحد, يظل على نفس السرعة, الجير مقفل على غيار
Some causes mean you should stop driving
5 of the 179 codes that produce this symptom indicate a fault where continuing to drive risks damage or is unsafe. If the symptom is sudden or severe, treat it as one of those until a scan says otherwise.
What this usually means
This is almost always the transmission protecting itself rather than a mechanical breakdown. Having lost a signal it depends on, the module selects one gear it can guarantee and stops shifting — commonly third or fourth, occasionally second. The car pulls away sluggishly and revs hard at speed, but it moves.
It is designed to get the vehicle home, not to be driven on, and the reason is heat. In that state the torque converter usually stays unlocked, so all the slip that lock-up normally removes is being turned into heat in the fluid, and the cooler was never sized to remove it continuously. A transmission already unsure of itself does not need the heat, so a long motorway journey in limp mode can turn a sensor fault into an overhaul.
Consistency is the distinguishing sign. A gearbox stuck in one gear every time, from cold, is behaving deliberately. A gearbox that changes gear sometimes and not others is a different and usually worse problem — slipping elements or falling pressure.
Try a restart, once. Some faults latch for an ignition cycle and clear on the next start. That does not fix anything; it tells you the fault is intermittent, which is a genuinely useful thing to know and is worth reporting.
Read the transmission's own codes, not the engine's. A generic reader that sees only powertrain codes will report a clean car, and this fault is reported by the transmission module.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Same gear every time, from cold, consistently | Limp mode — a deliberate, latched decision after a lost or implausible signal | Read transmission codes. Note which gear it holds; that narrows the circuit the module can still guarantee. | Diagnose the named fault. Do not drive far in this state — the unlocked converter is heating the fluid continuously. |
| Clears after an ignition cycle and returns later | An intermittent input rather than a failed component — the latch releases on restart | Restart once and note whether normal shifting returns. Log live data on a road test that reproduces it. | Repair what the log names. Static testing will find nothing on an intermittent, which is why the driver's account matters. |
| Speed sensor codes stored | The module cannot see what the transmission is doing, so it stops making shift decisions | Compare input and output speed live against road speed. A sensor reading zero while the car moves is the finding. | Renew the sensor or repair its wiring, checking the reluctor where one is used. |
| Fluid visible at the case connector or harness | Fluid wicking up the loom into the connector or module — a known path that produces electrical faults | Inspect the case connector directly. Fluid inside a connector is unmistakable once looked at. | Renew the seal and the affected harness section. Fitting a module without this repeats the failure. |
| Appeared with several other unrelated warning lights | Low system voltage rather than a transmission fault — the module misbehaves like any other | Test battery and charging before diagnosing the gearbox. Clear and re-scan after any supply repair. | Repair the supply first. Only what returns after clearing is a genuine transmission fault. |
| Changes gear sometimes and not others | Not limp mode — slipping elements or falling pressure, which is the worse case | Inconsistency is the discriminator. Measure line pressure hot and cold, and check fluid condition. | Diagnose as slipping rather than as a control fault. Stop driving it. |
-
Same gear every time, from cold, consistently
- Likely cause
- Limp mode — a deliberate, latched decision after a lost or implausible signal
- How to confirm it
- Read transmission codes. Note which gear it holds; that narrows the circuit the module can still guarantee.
- What fixes it
- Diagnose the named fault. Do not drive far in this state — the unlocked converter is heating the fluid continuously.
-
Clears after an ignition cycle and returns later
- Likely cause
- An intermittent input rather than a failed component — the latch releases on restart
- How to confirm it
- Restart once and note whether normal shifting returns. Log live data on a road test that reproduces it.
- What fixes it
- Repair what the log names. Static testing will find nothing on an intermittent, which is why the driver's account matters.
-
Speed sensor codes stored
- Likely cause
- The module cannot see what the transmission is doing, so it stops making shift decisions
- How to confirm it
- Compare input and output speed live against road speed. A sensor reading zero while the car moves is the finding.
- What fixes it
- Renew the sensor or repair its wiring, checking the reluctor where one is used.
-
Fluid visible at the case connector or harness
- Likely cause
- Fluid wicking up the loom into the connector or module — a known path that produces electrical faults
- How to confirm it
- Inspect the case connector directly. Fluid inside a connector is unmistakable once looked at.
- What fixes it
- Renew the seal and the affected harness section. Fitting a module without this repeats the failure.
-
Appeared with several other unrelated warning lights
- Likely cause
- Low system voltage rather than a transmission fault — the module misbehaves like any other
- How to confirm it
- Test battery and charging before diagnosing the gearbox. Clear and re-scan after any supply repair.
- What fixes it
- Repair the supply first. Only what returns after clearing is a genuine transmission fault.
-
Changes gear sometimes and not others
- Likely cause
- Not limp mode — slipping elements or falling pressure, which is the worse case
- How to confirm it
- Inconsistency is the discriminator. Measure line pressure hot and cold, and check fluid condition.
- What fixes it
- Diagnose as slipping rather than as a control fault. Stop driving it.
Codes that produce this symptom (179)
Listed with the codes that most typically present this way first — the likeliest place to start.
- P0702 Transmission Control System Electrical Typical of this code High
- P0715 Input/Turbine Shaft Speed Sensor A Circuit Typical of this code High
- P0717 Input/Turbine Shaft Speed Sensor A Circuit No Signal Typical of this code High
- P0720 Output Shaft Speed Sensor Circuit Typical of this code High
- P0722 Output Shaft Speed Sensor Circuit No Signal Typical of this code High
- P0725 Engine Speed Input Circuit Typical of this code High
- P0727 Engine Speed Input Circuit No Signal Typical of this code High
- P072F Stuck in Gear 4 Typical of this code Moderate
- P0733 Gear 3 Incorrect Ratio Typical of this code High
- P0748 Pressure Control Solenoid A Electrical Typical of this code High
- P0750 Shift Solenoid A Typical of this code High
- P0751 Shift Solenoid A Performance or Stuck Off Typical of this code High
- P0752 Shift Solenoid A Stuck On Typical of this code High
- P0753 Shift Solenoid A Electrical Typical of this code High
- P0755 Shift Solenoid B Typical of this code High
- P0756 Shift Solenoid B Performance or Stuck Off Typical of this code High
- P0757 Shift Solenoid B Stuck On Typical of this code High
- P0758 Shift Solenoid B Electrical Typical of this code High
- P0760 Shift Solenoid C Typical of this code High
- P0761 Shift Solenoid C Performance or Stuck Off Typical of this code High
- P0762 Shift Solenoid C Stuck On Typical of this code High
- P0763 Shift Solenoid C Electrical Typical of this code High
- P0765 Shift Solenoid D Typical of this code High
- P0767 Shift Solenoid D Stuck On Typical of this code High
- P0768 Shift Solenoid D Electrical Typical of this code High
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.
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