P0456 OBD2 Evaporative Emission Leak Detected in 2012 Dodge 2500 Truck - Is a New Gas Tank Really Needed?

A defective gas cap can only be confirmed through a proper gas cap tester or smoke test. These tests verify whether the cap seals correctly at the filler neck. Was a smoke test conducted to confirm either the cap or tank is leaking? Without such testing, it's difficult to pinpoint the source of the leak.

A smoke test was performed and showed leakage at the top of the fuel tank. However, during two prior visits to the same mechanic, no smoke test was done—only a detection valve replacement, which temporarily turned off the check engine light for one day. After replacing the gas cap, the light came back on after 2–3 days. My main concern is getting the light to stay off long enough to pass my vehicle inspection for registration renewal. I need this to be stable and reliable.

Even if the check engine light is off, it depends on how many readiness monitors are not fully completed. Since I live in Texas, emissions standards may differ from other states. It's questionable to recommend a full gas tank replacement without first inspecting for leaks—such as rust or cracks. The fuel tank has seals at key points: the fuel pump module and the fuel tank pressure sensor. Did the mechanic specifically state that the tank is corroded or damaged?

The P0456 fault occurs when, with the ignition off, fuel level is below 88%, ambient temperature between 4°C and 35°C (40°F to 95°F), and the fuel system is in closed loop. The Powertrain Control Module (PCM) monitors the Evaporative System Integrity Monitor (ESIM) switch. If the ESIM switch fails to close within a calibrated time, the PCM registers an error—this constitutes one trip fault. Three successful monitoring cycles are required before the MIL turns off.

I reside in Texas. The mechanic informed me that my fuel tank is made of plastic (polyethylene), which I had previously assumed was metal. This may impact how leaks are detected and addressed.

After the engine starts, the coolant temperature must be within 50°F (10°C) of ambient temperature to indicate a cold start. Fuel level should remain between 12% and 88%. The system must operate in closed loop mode. Manifold vacuum must exceed a minimum threshold, with ambient temperatures between 39°F and 98°F (4°C–37°C), and elevation below 8,500 feet. If you maintain fuel level above 88% and complete all readiness monitors, the system should pass—some states allow one monitor incomplete as long as the MIL is off. The evaporative emissions system includes a vapor recovery system with potential leak points: fuel tank pressure sensor O-ring, fuel pump module seal, and vapor recovery line. I can share a diagram if needed. If smoke is detected at the top of the tank, the tank should be slightly lowered during testing using UV-dye and UV light to pinpoint the exact location. A mechanic claiming a full tank replacement without lowering it or providing evidence of rust/cracks should be questioned.

The fuel tank is made of polyethylene plastic, not metal.