Driver's guide
Car symptoms: what they mean and what to do
A warning light, a noise, smoke or an odd smell is how a car tells you something is wrong. Find the symptom, see whether to stop now or book the workshop, and which fault codes usually come with it.
Reviewed by Daniel Morales, founder of Reprorace SL, on
When to stop now
These symptoms can cause serious damage or an accident if you carry on. Stop the car as soon as it is safe, switch off the engine and call for assistance:
- Flashing engine warning light: what it means and what to do
- Oil warning light on: what it means and what to do
- Engine temperature warning light on: what to do
- Red brake warning light on: what it means and what to do
- Smell of gasoline or diesel in the car: what to do
- Burning smell in the car: what it could be and what to do
- Knocking or pinking from the engine: what it means and what to do
- Soft, long or sinking brake pedal: what to do
- Exhaust fumes smell inside the car: why it is dangerous
A red warning light, smoke inside the car or a sudden loss of brakes or steering is always a reason to stop.
Symptoms by type
Warning lights
Red means stop or act now; amber or yellow, have it checked soon; green or blue only inform. Your car's handbook explains every symbol.
Flashing engine warning light: what it means and what to do
Stop as soon as it is safe
Engine warning light on and steady: what it means and what to do
Check without hurry
Oil warning light on: what it means and what to do
Stop as soon as it is safe
Battery warning light on: what it means and what to do
See a garage soon
Engine temperature warning light on: what to do
Stop as soon as it is safe
Airbag warning light on: what it means and what to do
See a garage soon
ABS or ESP warning light on: what it means and what to do
See a garage soon
Red brake warning light on: what it means and what to do
Stop as soon as it is safe
Tire pressure warning light on: what to do
See a garage soon
Electric parking brake warning light on: what to do
See a garage soon
Key or immobilizer light: the car does not recognize the key
Check without hurry
Service reminder or wrench light on the dashboard: what to do
Check without hurry
Low coolant warning light on: what to do
See a garage soon
Bulb failure or lighting warning light on: what to do
Check without hurry
Seat belt light will not go off: what it could be
Check without hurry
While the engine runs
Jerking, loss of power, an idle that hunts or an engine that stalls. Many of these faults store a code even when no light comes on.
Car jerks when accelerating: causes and what to do
See a garage soon
Car loses power: what limp mode is
See a garage soon
Rough idle: why the engine shakes or hunts when stationary
Check without hurry
Car stalls by itself: causes and what to do
See a garage soon
Engine runs rough when cold and fine when warm: what it could be
Check without hurry
RPM slow to drop when you lift off the gas: why
Check without hurry
Car overheats in traffic and cools down when moving: what is wrong
See a garage soon
Engine cooling fan will not stop: when it is normal and when not
Check without hurry
Smoke and smells
The color of the smoke and the kind of smell say a lot about what is burning or leaking. Some, such as fuel or burning plastic, mean stop.
White smoke from the exhaust: what it means and what to do
See a garage soon
Blue smoke from the exhaust: the engine is burning oil
See a garage soon
Black smoke from the exhaust: causes and what to do
Check without hurry
Smell of gasoline or diesel in the car: what to do
Stop as soon as it is safe
Burning smell in the car: what it could be and what to do
Stop as soon as it is safe
Rotten egg smell from the car: what it means
Check without hurry
Sweet antifreeze smell: what it means and what to do
See a garage soon
Exhaust fumes smell inside the car: why it is dangerous
Stop as soon as it is safe
Puddle under the car: how to tell which fluid is leaking
Check without hurry
Noises
A new noise almost always announces wear. Note when it appears: from cold, when turning, when accelerating or standing still.
Belt squeal when starting or turning: what it means
See a garage soon
Knocking or pinking from the engine: what it means and what to do
Stop as soon as it is safe
Noise when turning the steering wheel: what a click or a creak means
See a garage soon
Lifter tick or ticking engine noise: what it could be
Check without hurry
Turbo whistle when accelerating: when it is normal and when not
See a garage soon
Clunking noise over bumps: causes and what to do
See a garage soon
Exhaust louder than normal: what it means
See a garage soon
Humming noise that rises with speed: wheel bearing or tires
See a garage soon
Car vibrates when accelerating: what it could be
See a garage soon
Starting, battery and electrics
A car that will not start, takes long to start or has a flat battery in the morning. Telling whether the engine turns over is the first step.
Engine cranks but will not start: causes and what to do
Check without hurry
Car will not start and does nothing or just clicks
Check without hurry
Car slow to start: causes and what to do
Check without hurry
Car battery keeps going flat: causes and what to do
Check without hurry
Car will not start with a new battery: what it could be
Check without hurry
Lights, screens and comfort
Lights that flicker, a radio that switches off, a dashboard that blacks out or an A/C that blows warm. Many depend on the battery voltage and on the control units talking to each other.
Car lights flicker or dim: what is going on
See a garage soon
Power windows or central locking failing: what it could be
Check without hurry
Car radio or screen turns off by itself: why
Check without hurry
Instrument cluster goes dead or gauges fail: what to do
See a garage soon
Car A/C not blowing cold: what it could be
Check without hurry
Car heater not blowing hot: what it could be
Check without hurry
Fuel gauge reads wrong: what it could be
Check without hurry
Brakes and steering
These are safety systems: any change in the pedal or the steering wheel deserves a check as soon as possible, with no risks taken.
Noise when braking: what a squeal or a metallic grinding means
See a garage soon
Vibration when braking: why the steering wheel or pedal shakes
See a garage soon
Soft, long or sinking brake pedal: what to do
Stop as soon as it is safe
Car pulls to one side: causes and what to do
See a garage soon
Heavy steering or steering warning light on: what to do
See a garage soon
Steering wheel shakes at a certain speed: what it could be
See a garage soon
Gearbox and clutch
A jerky automatic, a slipping clutch or gears that are hard to select. The sooner it is checked, the cheaper the repair tends to be.
Automatic gearbox jerks: causes and what to do
See a garage soon
Slipping clutch: symptoms, causes and what to do
See a garage soon
Gears hard to engage or grinding: causes and what to do
Check without hurry
Automatic transmission warning light on: what it means
See a garage soon
Diesel: DPF, AdBlue and glow plugs
Modern diesels have systems of their own: particulate filter, AdBlue and glow plugs. Their warnings have their own way of being cleared.
Glow plug light on or flashing: what to do
Check without hurry
AdBlue warning light on: what it means and what to do
See a garage soon
Diesel particulate filter (DPF) warning light: what to do
See a garage soon
Particulate filter regenerating too often: causes
Check without hurry
Diesel will not start after running out of fuel: what to do
Check without hurry
Consumption
Using more fuel or more oil than usual is often the first sign of a fault you cannot see yet.
Car uses more fuel than normal: causes and what to check
Check without hurry
Car using oil: when it is normal and what to do
See a garage soon
Fault codes and guides
If the car has stored a fault code, its page explains what it means. These guides help you read it and decide what to do.
Car systems: how they work and what fails
Every car system explained one by one: engine, cooling, ignition, fuel, exhaust, turbo, transmission, brakes, steering, battery, CAN network and airbags.
OBD fault codes: what each one means
Glossary of OBD-II/EOBD fault codes (P, C, B and U) in plain English: what each code means, common causes, severity and whether you can keep driving.
Check engine light on: what to do
Your engine warning light has come on: what it means, when to stop, when you can drive to a workshop and how to find out which code the car has stored.
How to read and clear your car's fault codes
Where the OBD socket is, how to read your car's fault codes, how to interpret them and when to clear them (and when not to), in plain English.
In the glossary
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.
Frequently asked questions
Which warning lights mean I must stop the car?
The red ones: oil pressure, engine temperature, brakes, and battery charging if the temperature also rises or the steering goes heavy. Also the engine light when it flashes. Stop somewhere safe, switch off the engine and check the handbook or call for assistance.
Does an OBD reader tell me what is wrong with the car?
It tells you what the control unit has detected: the fault code, the data from the moment it happened and live data. It is the starting point, not the whole diagnosis: the same code can have several causes, and the garage checks them on the car.
Can there be a fault with no warning light on?
Yes. Many faults store a pending code before the light comes on, and noises, vibrations or brake problems hardly ever light it. If something feels wrong, have it checked even if the dashboard is clear.
Does clearing the code help to pass the MOT?
No. Clearing the code switches the light off, but the fault is still there and the readiness monitors stay incomplete until the car has done its drive cycles. The periodic inspection (the MOT in the UK) checks the light and can read those monitors.