What is a common cause of a failed emissions test indicated by a P0455 code?

A P0455 code indicates that there is a large leak in the evaporative emission control system (EVAP). One of the most common causes of this code is indeed a loose or damaged gas cap. The gas cap helps create a sealed environment in the fuel tank, preventing fuel vapors from escaping into the atmosphere. When the gas cap is not securely fastened or is cracked, it can lead to a significant leak that triggers the P0455 code during an emissions test.

In contrast, a failing ignition coil primarily affects engine performance, specifically related to misfires or poor power delivery, and does not directly relate to emissions testing linked to the EVAP system. Similarly, a leaking radiator is related to the cooling system rather than any emissions issues. An improperly balanced tire concerns vehicle handling and safety but does not influence emissions or trigger the P0455 code. Therefore, a loose gas cap is the most pertinent cause of the identified emissions failure.