On 1999–2004 Odyssey, P1457 points to the canister side of Honda's older EVAP system; P1456 points toward the tank side. Bulletin 99-075 Procedure A includes these Odyssey years and provides HDS function, FTP-sensor, valve and vacuum tests. A gas cap is not the default P1457 repair. Inspect canister plumbing, purge/vent/bypass sealing and pressure-sensor plausibility, then section the system. Later Odysseys use generic P044x logic and different components.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Use 99-075 Procedure A.
What can set P1457—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 |
|---|---|---|
| Canister-side hose leak/misrouting | Visual/smoke/vacuum result | Routing and sectional test |
| Vent/bypass valve leakage | Fails command/vacuum hold | Individual valve test |
| Purge valve leakage | Vacuum passes commanded closed | Closed-state sealing |
| Canister/two-way valve fault | Other sections pass | Procedure A isolation |
| FTP sensor bias | Atmospheric/commanded values implausible | Signal/reference test |
Honda divided the older EVAP system
P1456 and P1457 identify different regions.
Preserve that diagnostic direction instead of defaulting to a cap.
A valve can mimic a leak
The monitor expects valves to seal and route vapor in sequence.
A valve may click yet leak internally.
Procedure A matters
Honda groups Odyssey with Accord/Pilot for this architecture.
Using Civic/CR-V Procedure B substitutes different plumbing.
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 temperature
- P1456/electrical companions
- FTP value
- Purge/vent commands
- Recent tank/canister work
- Hose/corrosion evidence
A practical diagnostic workflow
- 01Confirm early system
Procedure A covers 1999–2004 Odyssey.
- 02Run function test
Preserve pass/fail and FTP behavior.
- 03Separate leak regions
P1457 is canister-side.
- 04Test valve sealing
Clicking alone is insufficient.
- 05Section safely
Use regulated smoke/vacuum.
- 06Complete monitor
Verify correct pressure behavior.
Do not call P1457 a guaranteed gas-cap code or replace a canister without isolating valves/hoses. Do not extend the bulletin to later years.
Why the model year changes the test
Odyssey diagnostics span several J35 V6 generations, port and direct injection, VCM cylinder deactivation, conventional and newer EVAP hardware, plus six cylinder-specific misfire codes and two catalyst banks. Confirm VIN, model year, engine/calibration, emissions label and current Honda warranty/campaign status. Do not transfer four-cylinder Accord, Civic or CR-V VTEC bulletins to this J35-powered minivan.
- 99-075 lists 1999–2004 Odyssey.
- P1457 is canister-side; P1456 tank-side.
- Later P044x layouts differ.
- FTP plausibility precedes leak conclusions.
P1457 FAQ
Is P1457 a gas-cap code?+
Not primarily; it is canister-side.
Which years are covered?+
1999–2004 in 99-075.
Can I drive?+
Usually briefly without odor/wet fuel.
What is P1456?+
The tank-side code on this system.
Does a click prove a valve?+
No; sealing and flow must be tested.
Can smoke help?+
Yes, safely regulated.
Does this apply to 2012?+
No; that system uses P044x codes.
What confirms repair?+
Correct FTP/valve behavior and completed 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.
01Honda Service Bulletin 99-075 — 1999–2004 Odyssey P1456/P1457Procedure A separates tank-side and canister-side leak diagnosis using HDS/FTP and valve tests↗02Honda ServiceExpressHonda VIN-specific diagnostics, wiring, bulletins and campaign status↗03Honda Owners — Odyssey manualsOfficial model-year warnings, maintenance and operating information↗