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Loss of power or limp mode

Sudden loss of power usually means the engine computer has found a fault and put the car into limp mode. Turbo, DPF, sensor and fuel problems are the usual causes.

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What limp mode is

When a modern car’s engine computer detects a serious fault, it can limit power and revs to protect the engine and gearbox. This is often called limp mode. You’ll usually see a warning light, and the car may feel stuck in one gear or unwilling to go above a low speed.

Common causes of losing power

Turbo problems

A split boost hose, a failing turbo or a sticking control valve can cause sudden loss of power, often with a whistle or a “whoosh” sound.

Blocked DPF or EGR valve (diesels)

A clogged diesel particulate filter or a sticking EGR valve restricts the engine and commonly triggers limp mode.

Sensor faults

A faulty air-flow, pressure or throttle sensor can give the computer wrong readings, so it cuts power to be safe.

Fuel supply

A blocked fuel filter, a failing pump or injector problems can starve the engine, especially under acceleration or uphill.

Misfires

A failing coil, plug or injector causes juddering and lost power. A flashing engine light means a misfire: reduce speed and get it checked straight away.

Gearbox problems

Automatic gearbox faults can also put the car into limp mode. See clutch or gearbox problems.

What to do

  1. If power drops suddenly on a fast road, move to a safe place as soon as you can. Don’t stop in a live lane unless you have to.
  2. Note any warning lights and messages, and whether the engine sounds or smells different.
  3. Switching off and restarting sometimes clears limp mode for a while, but the fault is still there and needs reading.
  4. Drive gently and directly to a garage only if the car is driving safely. Otherwise arrange recovery.

What a garage will do

A mechanic will read the fault codes, then test the suspect system: boost pressure, sensors, fuel delivery or ignition. A code points to where the fault was detected, so a good mechanic tests before replacing parts. Get a quote before agreeing to repairs.

Frequently asked questions

Can I drive in limp mode?

Only gently and for a short distance to get somewhere safe or to a garage. Limp mode is a warning that something is wrong.

Will limp mode clear by itself?

It may clear after a restart, but it will usually come back until the fault is fixed.

Why does my car lose power going uphill?

Often fuel supply, turbo or DPF problems, which show up most when the engine is working hardest.

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