Gearbox and clutch
Automatic transmission warning light on: what it means
The transmission light or message means its control unit has detected a fault, and it often locks the gearbox in a fixed gear to protect itself: the car moves, but pulls away weakly and revs high on the highway. It can be the transmission fluid, a sensor, a solenoid or the voltage.
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Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. Drive carefully to a shop without pushing it: in limp mode avoid highways and long climbs. If the message says the transmission is too hot, stop somewhere safe and let it cool with the engine idling or off, as the owner's manual says.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- High transmission fluid temperature: long traffic jams, towing or climbs; the warning usually clears once it cools.
- Fluid level or condition: low or degraded fluid changes the pressures.
- Speed or pressure sensors: without their signal, the control unit cannot shift properly.
- Solenoids: they control the shifts and wear or get dirty.
- Voltage or communication: a weak battery or a bad ground causes faults with nothing actually broken.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: What does a pending, stored or permanent code mean? What is live data and what is it for?
Car system: Transmission
What you can check yourself
See whether the message mentions high temperature: if so, stop and let it cool.
Switch the engine off for a minute and restart: sometimes it leaves limp mode, but the fault stays stored.
Note when it appeared: cold, hot, while shifting or while braking.
Look for reddish spots under the car.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- P0700Transmission control system: MIL illumination requested
- P0715Input/turbine shaft speed sensor A, circuit: malfunction
- P0730Incorrect gear ratio
- P0868Transmission fluid pressure: too low
- P0841Transmission fluid pressure sensor/switch A, circuit: range/performance
- P0882TCM power input signal: signal low
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: transmission fluid temperature, gear engaged and actual ratio, pressures if the car reports them and transmission codes.
Frequently asked questions
What is transmission limp mode?
The transmission stays in a fixed gear to protect its parts and let you reach a shop.
Can I clear the code and carry on?
You can clear it after noting it down, but if the fault is still there it will come back. Better to know the cause first.
Does automatic transmission fluid need changing?
It depends on the manufacturer: some call for it by mileage or heavy use, others do not. Check the maintenance schedule.
Keep reading
- Transmission: how it works and what fails
- Automatic gearbox jerks: causes and what to do
- Car loses power: what limp mode is
- Gears hard to engage or grinding: causes and what to do
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means