Honda P1456 Code: EVAP Control System Leakage (Fuel Tank System)
Honda's EVAP test found a vapor leak on the fuel tank side of the system.
Safety first · Consult a professional
- Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.
At a glance
Severity: Low
- Meaning
- EVAP Control System Leakage (Fuel Tank System)
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $15–$600
- DIY difficulty
- Easy
Honda splits its EVAP leak test into two halves: the fuel tank side and the charcoal canister side, separated by a two-way valve and a bypass solenoid. P1456 means the PCM sealed the system, watched the fuel tank pressure sensor, and saw the pressure or vacuum on the tank side leak away too quickly. The tank side includes the fuel cap, the filler neck, the hoses and valves on top of the tank, and the tank pressure sensor itself. A loose or worn fuel cap is by far the most frequent cause, but rusted filler necks and cracked vapor hoses are common on older Accords, Civics, CR-Vs and Odysseys.
Can I keep driving? The car is safe to drive and performance isn't affected. If you notice a raw fuel smell, don't ignore it; get the leak located soon and keep ignition sources away from the rear of the car.
How to read P1456
- P Powertrain
- 1 Manufacturer-specific
- 4 Auxiliary emission controls
- 56 Specific fault
Symptoms
- Check engine light on, often after refueling
- 'Check Fuel Cap' message on models that have it
- Faint fuel smell around the rear of the vehicle, especially after filling up
- No change in how the engine runs
- May be stored together with P1457 if the leak affects both halves of the system
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Fuel cap loose, cross-threaded, or with a hardened or cracked seal
- Rusted or cracked fuel filler neck, or leaking filler neck hose
- Cracked vapor hose or loose connection on top of the fuel tank
- Faulty EVAP two-way valve or bypass solenoid
- Faulty fuel tank pressure sensor
- Leaking fuel pump/sender seal or tank vapor valve
Diagnosis step by step
Check and reseat the fuel cap
Remove the cap, inspect the rubber seal for cracks or flattening, wipe the filler neck lip clean and reinstall it until it clicks. If the seal is damaged, fit a new cap from Honda or a quality equivalent; cheap caps often don't seal well enough for Honda's test.
Tools: Flashlight
Clear the code and monitor
Clear the code after fixing the cap and drive normally for several days. Honda's EVAP test needs specific conditions, including a cold start and a partly filled tank, so it may take a while to confirm the repair.
Tools: OBD-II scanner
Inspect the filler neck and tank-top hoses
With the car safely raised, inspect the filler neck for rust perforation, especially near the lower end, and check every vapor hose and quick-connector around the top of the tank for cracks. Work in a ventilated area with no sparks or flames nearby.
Tools: Flashlight, Gloves
Smoke test the tank side
A smoke test is the most reliable way to find EVAP leaks. Smoke is fed into the system with the vent closed, and the leak point shows where smoke escapes; small leaks at the filler neck or tank hoses are often invisible otherwise.
Tools: Smoke machine
Test the two-way valve, bypass solenoid and tank pressure sensor
A Honda-capable scan tool can command the bypass solenoid and vent shut valve and run an EVAP function test. With the fuel cap off and key on, the tank pressure sensor should read close to atmospheric; a reading that's clearly off points to the sensor.
Tools: OBD-II scanner, Multimeter
Where the parts are
- 1Gas cap
- 2Charcoal canister
- 3Purge valve
- 4Vent valve
- 5Fuel pump
- 6Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace fuel cap | Yes | $15–$45 |
| EVAP smoke test (diagnosis) | No | $100–$200 |
| Replace cracked vapor hose | No | $100–$300 |
| Replace EVAP two-way valve or bypass solenoid | No | $150–$400 |
| Replace fuel filler neck | No | $250–$600 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P1456 turns on the check engine light, so the vehicle fails a US OBD emissions test. After the repair, the EVAP monitor must show ready again, which can take several days of normal driving.
Frequently asked questions
Will a new gas cap fix P1456?
In many cases, yes; a worn or loose cap is the most common cause. If the code comes back after a new cap and a few days of driving, the leak is elsewhere on the tank side and needs a smoke test.
What's the difference between P1456 and P1457?
Honda splits the EVAP test into two sections. P1456 points to the fuel tank side (cap, filler neck, tank hoses, tank pressure sensor), while P1457 points to the charcoal canister side (canister, vent shut valve, purge lines).
Is it dangerous to drive with P1456?
The engine isn't affected. Most EVAP leaks are tiny vapor leaks, but a strong fuel smell means there's a bigger leak or a liquid fuel leak, which should be checked right away.
How long until the check engine light goes off?
After the repair, the light turns off once the EVAP test has passed on its own, which usually takes a few days of mixed driving including a cold start. Clearing it with a scan tool is quicker, but the monitor still has to complete before an emissions test.
Sources
- Manufacturer public service information (cross-checked)
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