P0456 on Acura: How to Diagnose & Fix
Evaporative Emission Control System Leak Detected (Very Small Leak)
1 Acura model · 1 documented issue · $40-$150 repair
P0456 on Acura by model: symptoms, diagnosis and fix
Second-generation RDX owners get a TIGHTEN FUEL CAP message and a check engine light for an EVAP leak, and the cap is tight. Acura issued service bulletin 14-006 covering the RDX and other Honda/Acura models: the original fuel cap's black gasket fails to seal reliably, so the EVAP system's leak monitor reports a leak that no amount of retightening will clear. Because the cap looks and feels fine, this is commonly chased with expensive smoke testing and purge-valve replacement before the cap is suspected. The EVAP fault will also block emissions-test readiness monitors.
Common Symptoms
- TIGHTEN FUEL CAP message on the dash
- Check engine light with EVAP leak code
- Code returns after retightening or replacing with a generic cap
- Emissions readiness monitors will not set
How to Fix
Replace the fuel cap with the updated OEM cap — the revised part carries a brown gasket rather than the original black one — per TSB 14-006, then clear the code and allow the EVAP monitor to run to completion. This is a low-cost fix and should be the first step before smoke testing. If the code returns with the revised cap installed, smoke-test the system for a cracked EVAP canister or a failed purge/vent valve, both documented on this platform. There is no recall.
Sources for this issue (2)
P0456 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0456 mean on a Acura?
P0456 stands for "Evaporative Emission Control System Leak Detected (Very Small Leak)." This emissions code means the evaporative emission (EVAP) control system has detected a very small leak — even tinier than the one flagged by P0442, roughly equivalent to a 0.020-inch hole. The EVAP system traps fuel vapors from the tank and prevents them from escaping into the atmosphere, and the computer tests for leaks by sealing the system and watching for pressure or vacuum loss. Because the leak is so small, the cause is often subtle, but a loose or worn gas cap is still the most common and easiest to check. It generally indicates a minor seal, hose, or valve leak somewhere in the fuel vapor system. On Acura it is documented across 1 model: RDX.
What are the most common causes of P0456?
The most common causes of P0456 are: Loose, worn, or faulty gas cap or cap seal, Cracked or loose EVAP hose or line, Leaking vent valve or purge valve not sealing, Damaged O-ring or seal at the fuel filler neck, Small crack or leak in the charcoal canister, Leaking fuel tank or sending unit gasket, Loose or corroded EVAP component connection. The specific cause varies by vehicle.
How much does it cost to fix P0456 on a Acura?
Published repair estimates on Acura range from $40 to $150 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0456 on a different make?
View P0456 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.