The P0455 code on your 2019 Ram 2500 indicates the PCM has detected a gross (large) leak in the evaporative emission system. Unlike small leak codes, P0455 means there's a significant opening in the system allowing major vapor escape.
What Constitutes a Gross Leak
A gross leak is typically 0.040 inches or larger—a substantial hole in the sealed EVAP system. These leaks are usually easier to find than small leaks because they're physically larger. The system essentially has a major breach.
Ram 2500 EVAP System
The 2019 Ram 2500 offers the 6.4L HEMI gas engine or 6.7L Cummins diesel. Both have EVAP systems, though diesel systems operate differently. The heavy-duty truck's large fuel tank and extended vapor lines create more potential leak points.
Gross Leak Sources
Missing or incorrectly installed gas cap is the most common cause. Disconnected EVAP hoses are obvious sources. Cracked or broken charcoal canister. Major damage to vapor lines from road debris. Improperly sealed fuel tank filler neck. After fuel system service, components may be left disconnected.
Finding the Leak
Check the gas cap first—is it present, properly threaded, and sealing? Listen for hissing sounds near the fuel system. Visually inspect all EVAP hoses and connections. Look for obviously disconnected or broken components. Smoke testing can quickly reveal gross leaks since the smoke escapes prominently.