Fault finding by symptom

How this works

Pick the symptom that fits best. You see possible causes, what you can safely check yourself and when to stop. No artificial intelligence or paid model is used: these are fixed rules.

Draft and not professional advice. A symptom often has several causes. If in doubt about safety: do not drive and call a garage or breakdown service.

The car does not start

Only a click or nothing, dim lights: usually a flat or weak battery or a loose battery clamp. Engine turns but does not fire: possibly fuel, ignition or a sensor.

• Is the gearbox in P or N, and is the pedal pressed where required?
• Are the battery clamps tight and clean?
• Is there fuel, or charge in an electric car?
• Is an immobiliser light or another warning light on?

If you smell fuel or see smoke, do not keep trying to start.

The engine overheats

Possible causes: too little coolant, faulty thermostat, faulty water pump or fan, a leak in the cooling system.

1. Stop safely and switch the engine off.
2. Wait until the engine has cooled and never open the cooling system cap while the engine is hot.
3. Check the coolant level and look for leaking fluid.
4. If the temperature keeps rising, do not drive on and call breakdown service.

Brakes squeal, grind or feel soft

Squealing can indicate worn pads or dirt. A grinding metal-on-metal sound indicates worn-out pads and damaged discs. A soft or sinking pedal can point to air or a leak in the brake system.

A soft or sinking brake pedal, pulling to one side when braking or a brake warning light: do not drive on. Have the car taken to a garage.

Vibration in the steering wheel or car

Vibration at certain speeds often points to unbalanced wheels, a bulge in a tyre or damaged rims. Vibration when braking often points to warped brake discs. Pulling to one side can be wrong tyre pressure or poor alignment.

• Check the pressure of all four tyres.
• Look for bulges, cracks or uneven wear on the tyres.
• Note when it vibrates: speed, braking or accelerating?

Smoke from the exhaust

White vapour on a cold start is often condensation and disappears. Persistent white smoke with a sweet smell can be coolant in the engine. Blue smoke points to oil burning. Black smoke points to an overly rich fuel mixture.

Persistent white smoke with rising temperature: stop and switch the engine off.

Rough idle or hesitation

Possible causes: spark plugs or coils, dirty air filter, vacuum leak, sensor fault or dirty fuel injection. A flashing engine light points to misfires that can damage the catalytic converter.

1. Have the fault codes read (see also the guide on OBD codes).
2. Check the air filter and tank cap.
3. With a flashing engine light: limit driving and have it checked quickly.

Noises or a burning smell

Clicking in turns can be a worn drive shaft. Whining when steering can be a power steering or belt problem. A burning smell can be an overheated brake, clutch or an electrical short.

If you smell burnt plastic or see smoke under the bonnet: stop, switch the car off and get out. Call 112 if needed.