Honda Civic Service Manual: Engine Cooling

Engine

...

Coolant Replacement (R18A9)

1. Radiator Cap 1. Wait until the engine is cool, then carefully remove the radiator cap. ...

See also:

Honda Civic Owners Manual. With Little Chance of a Collision
The CMBSTM may activate even when you are aware of a vehicle ahead of you, or when there is no vehicle ahead. Some examples of this are:  When Passing Your vehicle approaches another vehicle ahead of you and you change lanes to pass.  At an intersection Your vehicle approaches or pa ...