Phrasal verb: Act up (meaning, examples, pronunciation)

"Act up" means "to malfunction or operate incorrectly."

Example #1: My car acted up again this morning. I don't know what's wrong with it.

Example #2: My computer's acting up - I think I might have a virus.

Example #3: The thermostat suddenly started acting up, and now it's always too hot or too cold in here.

Example #4: Has your internet been acting up today? Mine keeps cutting off!