Warning lights use color for a reason. Red generally means stop safely and shut the engine off; amber or yellow generally means have it checked soon. Knowing the difference keeps a cheap repair from becoming an expensive one.
Red: stop when it is safe
Oil pressure, engine temperature, charging system, and brake warning lights belong in this group. Continuing to drive with oil pressure or overheating warnings on can cause damage in minutes. Pull over where it is safe, shut the engine off, and call for help.
Amber: have it checked soon
The check engine light, tire pressure light, and most system-fault lights are amber. The car usually still drives, but a stored fault can affect fuel use, emissions, and other components. A steady check engine light means schedule a diagnostic; a flashing one means bring it in right away.
What to tell us when you call
Describe the light's color, whether it is steady or flashing, when it appeared, and anything that changed at the same time — a noise, a smell, rough running, or a loss of power. Those details shorten the diagnostic path considerably.
Why code readers are only a start
A stored code names the circuit or system reporting a problem, not the failed part. Proper diagnosis tests the components in that circuit so the repair addresses the actual cause instead of replacing parts in sequence.