Warning lights are the car's way of telling you something needs attention. When you're buying used, they're also one of the quickest ways to spot a problem.
The important ones
✓Check engine: the engine management system has detected a fault. It could be minor or serious, and a diagnostic scan is needed to know which.
✓Oil pressure: low oil pressure can quickly damage an engine. Stop driving if it comes on.
✓Battery or charging: the charging system has a fault. The alternator and battery are the first things to check.
✓Coolant temperature: the engine is running hot. Continuing to drive can cause major damage.
✓Brake system: low brake fluid or a brake system fault.
✓ABS: the anti-lock braking system has a fault. Standard braking keeps working, but anti-lock protection is switched off until the fault is fixed.
✓Airbag (SRS): the airbag system has a fault, and the airbags are not guaranteed to deploy in a crash.
Check the bulb check
When you turn the ignition on, most warning lights should briefly illuminate, then go out once the engine starts. A light that never comes on at all is a sign the bulb or circuit has been disabled to hide a fault.
Recently cleared codes
Fault codes can be cleared with an inexpensive scan tool, which turns the light off until the fault is detected again. A professional diagnostic scan can help show whether codes have been cleared recently.
Never accept 'it's just a sensor' as an explanation without a diagnostic scan to confirm it.General information only. For advice on a specific vehicle, book an inspection with a licensed mechanic.