OBD-II code P1457 indicates the engine control module could not generate the expected vacuum level inside the fuel tank during the evaporative emissions (EVAP) system self-test. The most common underlying problem is a leak somewhere in the EVAP system or a fuel-vapor component that will not seal properly, allowing air to enter and preventing the tank from holding a vacuum.
A cap that does not seal tightly is the single most common cause of P1457 and is the correct first item to inspect before going further.
Rubber lines between the tank, canister, and valves can split, collapse, or pull loose from their fittings, allowing air to leak in during the vacuum test.
If the vent valve will not close fully when commanded, the tank cannot be sealed off and vacuum cannot be developed.
A purge valve stuck open, or a leak between the purge valve and intake, prevents the system from holding the target vacuum.
Liquid fuel in the canister or physical damage from a rear-end impact can create a leak path or block airflow in a way that disrupts the vacuum test.
PCM failure is a rare cause of P1457; the controller is usually the last thing to suspect once all hoses, the cap, and the EVAP valves have been ruled out.
The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:
Yes, in most cases the vehicle will run normally. The code is emissions-related and does not typically affect drivability, but it will usually cause an emissions inspection failure until repaired.
Yes. A loose, missing, or degraded fuel filler cap seal is one of the most common causes of P1457 and should always be checked first because it is the simplest and cheapest fix.
Almost never. The PCM is replaced incorrectly for this code far more often than it should be. The overwhelming majority of P1457 faults are caused by the fuel cap, EVAP hoses, or the vent or purge valve, and a working PCM will simply flag the system as failing the vacuum test.
The standard method is a smoke test of the EVAP system, which introduces visible smoke into the sealed system so the leak point becomes easy to see. Electrical testing of the vent and purge valves is done alongside it.