P0456 · Very small evaporative emissions system leak
P0456 means your car detected a very small leak in the system that keeps fuel vapors from escaping. A loose gas cap can set this code, and so can a leak elsewhere in the system.
Part of the EVAP system guide.
Could it be the gas cap?
With the car parked and the engine off, check that the cap is seated properly. Look for a cracked seal or dirt where it meets the filler neck. On a capless car, look for visible debris around the opening and follow the manual’s instructions for clearing it. A fill-up is a useful clue, but the car can take time to run the leak test, so the timing alone doesn’t tell you where the leak is.
If the filler looks fine
Ask the shop how it will find the leak before it quotes a part. A smoke test with equipment made for fuel vapor systems can help locate a leak at a hose, seal or valve. The shop may also need to check whether the purge or vent valve closes all the way.
On the Nissans covered by bulletin NTB17-082E, the technician checks where the vent valve joins the canister after ruling out the fuel cap. The bulletin calls for replacing the valve assembly once a leak at that seal is confirmed.
P0456, P0442 and P0455
All three point to an EVAP sealing problem. P0456 describes a very small leak, P0442 a small leak, and P0455 a large leak or a failure to seal. Save all the codes if more than one shows up. None gives the shop the location of the leak.
Will the light go off after I tighten the cap?
It may stay on until the car has another chance to run its EVAP test. The conditions depend on the vehicle. Leave the codes in place so you can see what comes back, and check the EVAP monitor’s readiness if you’re due for an emissions inspection.