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

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.

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 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.

The Dodge Challenger's evaporative emissions (EVAP) leak-detection device — the Evaporative System Integrity Module/Monitor (ESIM), the successor to Chrysler's older NVLD (Natural Vacuum Leak Detection) pump — is a very common failure point across the LX/LA platform (2008-2023). The ESIM is a mechanical, non-solenoid device (housing, two check valves/weights, a diaphragm, and a switch) bolted to the charcoal canister behind the rear passenger fender-well liner. It performs an engine-off non-intrusive test for small leaks and an engine-running test for medium/large leaks, and the PCM relies on it for ALL EVAP leak diagnostics. When the ESIM's diaphragm or switch fails, the PCM falsely concludes the sealed EVAP system is leaking and sets P0456 (small leak), P0455 (large leak), or a generic P0440, illuminating the check-engine light. Because the code description points to a leak, the part is repeatedly misdiagnosed: owners and shops replace the gas cap (sometimes multiple times), get a clean smoke test showing no actual leak, yet the code returns. Multiple forum threads document owners chasing this for months — replacing the gas cap, then the purge/canister valve — before the ESIM ("vapor leak detection pump") is finally identified as the real fault. One owner reported spending roughly $2,500 over repeated visits before the issue was resolved. In some cases the leak-detection pump was simply found unplugged behind the wheel-well liner.

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.