P0455 means the Charger EVAP system could not establish or retain the expected seal. Inspect the cap or capless filler without disturbing evidence, test purge and ESIM/vent valves for actual sealing, and smoke-test rear lines, canister and top-of-tank connections at regulated pressure. A disconnected hose and a valve held open can look identical to the PCM. P0456 software bulletins do not automatically apply to this larger-leak code.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Record cap/filler state.
What can set P0455—and how to separate it
The order below is evidence-driven, not a universal probability ranking. Vehicle year, repair history, companion codes and the operating condition in freeze frame change where diagnosis should begin.
| Possible cause | Evidence that supports it | First useful test |
|---|---|---|
| Missing/loose/damaged cap or filler | Found condition/seal test | Filler inspection |
| Purge valve stuck open | Vacuum passes commanded closed | Sealing test |
| ESIM/vent or disconnected hose | Cannot seal/smoke exits | Function and smoke test |
| Canister, tank or pump seal leak | Sectional smoke | Low-pressure test |
| Leak-detection circuit fault | Implausible data/companion code | Circuit/function test |
A large leak may be an open normal passage
The purge and vent paths are designed to open during normal operation, so either valve held open can prevent the test from sealing. Commanding a solenoid and hearing a click only proves movement or current, not leak-tight closure.
Isolate purge from the manifold and verify closed-state flow, then operate the leak-detection or vent device according to the exact service procedure. This prevents an expensive tank search when a front-of-car valve is the open path.
Follow recent work along the rear of the car
Charger vapor lines cross a low underbody and terminate around the rear canister and tank. Inspect displaced clips, crushed tubing, road impact and quick-connects after exhaust, rear suspension, collision or fuel-pump work.
Use EVAP-safe regulated smoke and section the system so the plume identifies a component boundary. Unrestricted shop pressure risks damaging the canister or tank and can turn a diagnostic job into a safety problem.
Verify the monitor, not only the absence of smoke
A repaired gross leak may still require an overnight soak and a permitted fuel-level range before the PCM reruns its monitor. Preserve pending-code and readiness status instead of repeatedly clearing memory.
If no physical leak is found, validate pressure-switch or ESIM data and circuit integrity using the correct model-year schematic. A false leak-detection signal must be proven; replacing the PCM or canister by elimination is not a test.
Save these scan-data clues
Freeze frame is a snapshot of conditions when the PCM matured the fault. It can distinguish an idle-only problem from a load, cold-start or monitor-completion problem. Clearing first throws that context away.
- Exact VIN, platform, model year and engine sales code
- All confirmed, pending and permanent companion codes
- RPM, load, coolant temperature and vehicle speed
- Relevant commanded and actual scan data
- Recent service, repairs and symptom conditions
- Manufacturer bulletin and current software/VIN status
A practical diagnostic workflow
- 01Identify platform
Routing differs.
- 02Preserve evidence
Record filler before changing.
- 03Test purge and ESIM/vent
Clicking is not sealing.
- 04Smoke safely
Section tank, canister and filler.
- 05Validate detection data
Circuit faults can imitate leakage.
- 06Complete monitor
Meet fuel/soak conditions.
Do not replace the most commonly named component from P0455 alone. Confirm the exact engine, preserve evidence and complete the manufacturer test sequence before ordering parts.
Why the model year changes the test
Modern Charger diagnostics span LX and LD rear-wheel-drive platforms, optional AWD and 2.7L, 3.5L, 3.6L Pentastar, 5.7L HEMI, 6.1L and 6.4L engines. Cylinder banks, oil-pressure control, cam sensing, EVAP plumbing and catalyst locations are not interchangeable. Confirm model year, VIN, engine sales code, build date and current PCM calibration before applying any test value, bulletin or diagram.
- EVAP routing changes across LX/LD years and fuel-system revisions.
- Rear collision, exhaust or fuel-pump work can disturb vapor lines.
- Hard starting after refueling increases purge-leak priority.
- Strong vapor odor or liquid fuel requires stopping and safe inspection.
P0455 FAQ
Is it always the cap?+
No.
Can I drive?+
Usually briefly without odor or wet fuel.
Can purge cause hard start?+
Yes.
Can tank service cause it?+
Yes, through seals or disconnected lines.
Can I use shop air?+
Not unregulated.
Why did a new cap fail?+
The fault may be elsewhere.
Does a P0456 flash apply?+
Not automatically to P0455.
What confirms repair?+
Passing leak test and monitor.
Ford diagnostic references
These documents explain Ford monitor operation. Exact pinpoint tests, connector views and specifications must be selected for the truck's VIN and model year in current service information.
01Mopar vehicle informationOfficial owner manuals and model-year engine, oil, warning and operating information↗02Stellantis/Mopar service informationFactory VIN-, platform-, engine-sales-code and calibration-specific service information↗