When the fire apparatus is using only emergency lights and no audible sirens, it is engaging in a:

A fire apparatus that is using only emergency lights without audible sirens is engaging in a Code 2 response. This type of response indicates that the vehicle is responding to an emergency situation but is not requiring the immediate clearance of traffic, which would necessitate the use of both lights and sirens.

The use of emergency lights alone can be appropriate for certain situations where a more subdued approach is needed, such as when responding to a call in a residential area, to avoid startling residents, or when traffic is light enough that the lights alone can effectively alert other drivers.

In contrast, other responses like Code 1 would indicate no lights or sirens being used, Code 3 would involve both lights and audible sirens for a high-priority emergency requiring immediate clearance of the roadway, and a silent response typically denotes no activation of emergency response signals.