P0455 means the Wrangler's EVAP monitor found gross loss of sealing or failed pressure behavior; it does not identify the opening. Record cap/filler condition, fuel level, recent fuel-pump/tank work and companion circuit codes. Test purge closed-state sealing, vent/ESIM behavior and use regulated smoke to section hoses, canister, filler and top-of-tank seals. TJ, JK and JL component names and layouts differ. P0456 software bulletins do not automatically apply to P0455, and software cannot repair a disconnected hose.
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 commanded closed | Sealing test |
| ESIM/vent or disconnected hose | Cannot seal/smoke exits | Command/smoke test |
| Canister/tank/pump seal leak | Sectional smoke | Low-pressure test |
| Pressure/leak-detection circuit fault | Implausible data/companion code | Circuit/function test |
Large leak can be a normal path held open
Purge/vent passages must close during test.
A stuck valve imitates a broken tank.
Off-road packaging matters
Mud, impact and skid/tank service can affect lines and canister hardware.
Inspect before electrical replacement.
Platform controls the schematic
Names, locations and test methods changed from TJ to JL.
Use VIN/platform-specific routing.
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.
- Fuel level/soak
- P0456/P044x circuit codes
- Leak-detection data
- Purge command
- Filler found state
- Recent tank/body work
A practical diagnostic workflow
- 01Identify platform
TJ/JK/JL routing differs.
- 02Preserve evidence
Record cap/filler before changing.
- 03Test purge and vent/ESIM
Clicking is not sealing.
- 04Smoke safely
Section tank/canister/filler.
- 05Validate detection data
Sensor/switch faults can imitate leakage.
- 06Complete monitor
Verify under fuel/soak conditions.
Do not buy cap, purge and ESIM together. Test each. Do not apply P0456 flash bulletins to an isolated P0455 without explicit applicability.
Why the model year changes the test
Wrangler spans YJ/TJ 2.5L and 4.0L engines, JK 3.8L and 3.6L Pentastar, JL 2.0L turbo, upgraded 3.6L, 4xe hybrid, 3.0L diesel and 6.4L applications. Oil systems, cylinder banks, cam sensors, EVAP leak detection and catalyst layouts differ. Confirm platform (TJ/JK/JL), VIN, model year, engine/sales code, market and PCM software level before applying a bulletin or parts recommendation.
- TJ, JK and JL use different leak-detection hardware.
- 2018 overlap requires platform identification.
- Tank skid/off-road damage and post-service seals deserve inspection.
- P0455 is larger-leak logic than P0456.
P0455 FAQ
Always gas cap?+
No.
Can I drive?+
Usually briefly without odor/wet fuel.
Can purge cause hard start?+
Yes after refueling.
Can off-road damage matter?+
Yes, to lines/canister/tank.
Use shop air?+
Not unregulated.
Why new cap failed?+
Leak/valve is elsewhere or filler damaged.
Does P0456 flash apply?+
Not automatically.
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 information and owner manualsOfficial Wrangler operating, warning, engine-oil and model-year identification information↗02Stellantis/Mopar service informationFactory service, recall and vehicle information access; use VIN and engine sales code↗