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 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 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. Ford covered the affected build range under safety recall 15V793 (Ford 15S34) because the faulty purge valve can cause abnormal fuel-tank pressure changes that may crack the tank and leak fuel.

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.

The EVAP canister purge valve sticks open, causing difficulty fueling (pump nozzle keeps clicking off), rough idle, and check engine light. Very common on the 1.6L engine.