P0457: How to Diagnose & Fix — Evaporative Emission System Leak Detected (Fuel Cap Loose/Off)

A very common and frequently misdiagnosed problem on the Dodge Charger is failure of the EVAP (evaporative emissions) leak-detection device, which causes the PCM to log P0456 (small EVAP leak), P0455 (large EVAP leak), and/or P0457 (leak detected / fuel cap loose) and illuminate the check-engine light. On 2011-and-newer Chargers the system uses an ESIM (Evaporative System Integrity Module) — a natural-vacuum-based switch (the same NVLD-style monitoring concept) mounted directly on the charcoal/EVAP canister behind the passenger-side rear wheel well. With the EVAP system sealed, the PCM watches the ESIM/NVLD switch; if the switch's internal mechanical diaphragm fails or its external O-ring seal degrades, the switch fails to close within the calibrated time and the PCM falsely reports an EVAP leak. The classic giveaway is that a smoke test shows NO actual leak yet the code keeps returning. Because the code is almost always assumed to be a loose or failed gas cap, owners (and shops) often chase the wrong part first — replacing the gas cap and purge valve before discovering the real culprit is the inexpensive ESIM module. The code is low-severity (no driveability or engine damage, only a slight fuel-economy effect) but will fail an emissions/smog test and leaves the CEL on. In a worst-case escalation, the same codes can be caused by a pinhole leak on top of the fuel tank near a fuel-pump lock ring, which requires fuel-tank replacement. On 2022+ cars, Mopar TSB 18-094-23 addresses an over-sensitive EVAP monitor that can falsely set P0455/P0456/P0440/P0441 and is corrected with a PCM software update rather than a part.

The Chrysler 300 uses Chrysler's proprietary natural-vacuum leak detection hardware instead of a conventional pressure-based leak detection pump. On 2005-2006 cars this is the NVLD (Natural Vacuum Leak Detection) valve/solenoid; from 2007 onward it is the ESIM (Evaporative System Integrity Monitor), a small spring-and-diaphragm switch mounted on or next to the charcoal/vapor canister on the left underbody ahead of the fuel tank. Both work the same way: as the sealed EVAP system heats and cools, natural pressure/vacuum changes trip an internal switch the PCM reads to confirm the system is sealed. The diaphragm seal inside the NVLD/ESIM is a well-documented high-failure item — it stiffens, sticks, or loses its seal with age, so the PCM can no longer verify integrity and falsely reports a leak. The result is a check-engine light with P0456 (small leak, ~0.020 in.), P0455 (large leak), or P0457 (interpreted as loose/missing cap), even when the fuel system is actually sealed. Because the code wording points at the gas cap, this is very commonly misdiagnosed: owners and shops replace the cap (and often the purge valve and canister) repeatedly before discovering the NVLD/ESIM itself is the culprit. One 2012 300 SRT owner reported eight dealer visits — the ESIM and its seal replaced twice, plus a new filler neck, purge valve, and charcoal canister — before the leak code was resolved. The fault is an emissions/MIL issue only: it does not affect drivability or engine longevity, but it will fail an emissions/smog inspection and on some model years can disable remote start until cleared. A faint fuel-vapor smell is occasionally reported when an actual leak is present.

The under-hood evaporative-emissions purge valve on 2010-2011 Fusion/Milan (2.5L DOHC and 3.0L) built on or before 3/4/2011 can stick open or leak, unmetered vapor entering the intake. This lights the MIL and sets a cluster of EVAP and lean/fuel-trim codes, and can cause rough idle or hard starts. It is a documented Ford pattern failure with a related TSB covering the affected build range.

S197 Mustangs from the mid-2000s have a documented pattern of fuel tank cracking or leaking, often near the seam or around the evaporative emissions components. Owners report strong fuel odor in garages, visible dripping after fill-ups, and EVAP-related warning lights. Because the issue involves fuel leakage near the rear of the vehicle, it presents a fire risk and can require full tank replacement.

The Jeep Grand Cherokee uses a Natural Vacuum Leak Detection (NVLD) approach for its EVAP system, implemented through the Evaporative System Integrity Module (ESIM) — commonly called the leak detection pump. The ESIM is a standalone unit (typically mounted on the charcoal canister near the rear driver-side wheel well) that seals the fresh-air vent and uses natural temperature-induced pressure changes to verify the fuel-vapor system holds vacuum. The internal seal/diaphragm and check mechanism in the ESIM are a well-documented common failure point on Chrysler/Jeep platforms. When the unit fails, the PCM cannot complete its EVAP self-test and falsely reports an EVAP leak, illuminating the check engine light even though no actual leak exists. Because the same codes are thrown by a loose or worn gas cap, the failure is frequently misdiagnosed: owners (and even shops) replace the gas cap first, the light returns, and the actual ESIM/leak-detection-pump fault is missed. A simple field test is to remove the ESIM and shake it — a rattle indicates the internal valve has come loose and the unit needs replacement. Note that the EVAP purge-valve hose on top of the engine also becomes brittle and cracks (covered by Jeep TSBs #25-002-15 REV-B and #18-035-20), producing the same codes, so the hose should be inspected before condemning the ESIM. This is an emissions-only fault: it does not harm the engine or transmission but will fail a state emissions/smog test.