While the engine runs
Car loses power: what limp mode is
When the control unit detects a fault that could damage the engine or the gearbox, it limits power and engine speed: this is limp mode. The car drives, but slowly and without pulling power, and the engine or gearbox warning light usually comes on.
See a garage soonWhile the engine runs
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. It is meant to get you to a garage, not to finish the journey. Avoid overtaking and fast roads if you cannot keep up with traffic. If a red warning light also comes on, the temperature rises or there is smoke, stop as soon as it is safe.
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
- Wrong boost pressure: a loose hose, a valve or the turbo actuator; very common on diesels.
- Accelerator pedal or throttle sensors: if the two signals disagree, the control unit limits power for safety.
- Blocked particulate filter: with too much soot the engine protects itself by cutting power.
- Low fuel pressure: filter, pump or pressure regulator.
- Automatic gearbox fault: the gearbox locks into one gear to protect itself.
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: Why does my car go into limp mode when it is cold? What does the throttle body do and why does a fault trigger limp mode? How does a turbocharger work and what does P0299 mean?
Car system: Fuel and air
What you can check yourself
Find a safe place, switch the engine off for a couple of minutes and restart: power often returns, but the code stays stored.
Note which warning lights come on.
With the engine cold, look for a loose or split turbo hose.
Read the code before clearing it: it explains why the car protected itself.
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
- P0299Turbocharger/supercharger A: underboost
- P0234Turbocharger/supercharger A: overboost
- P2106Throttle actuator control system: forced power limitation
- P2110Throttle actuator A control system: forced engine speed limitation
- P0087Fuel rail/system pressure: too low (bank 1)
- P0101Mass or volume air flow sensor A, circuit: range/performance
- P0700Transmission control system: MIL illumination requested
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: requested and actual boost pressure, pedal and throttle position, fuel pressure and engine load.
Frequently asked questions
Power comes back after switching off and on. Is that it?
No: the control unit tests the system again, and if the fault is intermittent it will return. The code stays stored for the garage.
Can I make a long trip in limp mode?
It is not advisable: you lack the power to join traffic or overtake safely, and the fault can get worse.
Does limp mode damage the car?
No: it is a protection. What can damage it is the cause, if it is not repaired.
Keep reading
- Fuel and air: how it works and what fails
- Car jerks when accelerating: causes and what to do
- Diesel particulate filter (DPF) warning light: what to do
- Black smoke from the exhaust: 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