Lights, screens and comfort
Car lights flicker or dim: what is going on
If the lights flicker or dim, especially at idle or when you switch on accessories, the car's voltage is unstable. The usual causes are an alternator that charges poorly, a worn battery, a slipping belt or a ground with poor contact.
See a garage soonLights, screens and comfort
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. See a shop soon. If the battery light also comes on, the steering gets heavy or the engine runs badly, drive as little as possible: the car can lose power on the move. Avoid driving at night if the headlights dim a lot.
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
- Alternator or regulator: the voltage rises and falls or does not reach charging level.
- Worn battery: it no longer absorbs current peaks.
- Accessory belt: if it slips, the alternator does not spin properly.
- Grounds or terminals: a poor contact causes intermittent voltage drops.
- Battery management: on some cars the voltage varies on purpose to save fuel; it is slight and normal.
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: How can you tell if the 12 V battery is failing? Why is stop-start not working?
Car system: Electrical system and battery
What you can check yourself
Notice whether it happens at idle, when accelerating or when you turn on the rear defroster, the blower or the A/C.
Check the condition of the belt with the engine off.
See whether the battery terminals are loose or corroded.
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
- P0562System voltage: too low
- P0563System voltage: too high
- P0620Generator, control circuit: malfunction
- P0622Generator field/F terminal, circuit: malfunction
- U3003Battery voltage: malfunction
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: live system voltage at idle and with accessories on, alternator charging and voltage codes.
Frequently asked questions
Is it normal for the lights to dim a little when starting?
Yes, while cranking. Flickering with the engine running is not normal.
Can it be the battery even if it is new?
Less likely, but a loose terminal has the same effect.
Do LED lights flicker for another reason?
An unsuitable LED lamp can flicker even with the right voltage. If only one light is affected, start there.
Keep reading
- Electrical system and battery: how it works and what fails
- Battery warning light on: what it means and what to do
- Belt squeal when starting or turning: what it means
- Car radio or screen turns off by itself: why
- 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