P0440

Technical Summary

P0440 is defined as Evaporative Emission Control System Malfunction. The PCM runs one or more EVAP integrity and rationality checks using purge control, vent sealing, fuel-tank pressure change, leak-detection pump operation, or natural vacuum behavior. P0440 sets when the overall system fails to seal, respond, or operate as expected but the monitor does not isolate a more specific fault. The monitor may use engine vacuum, a leak-detection pump, natural vacuum after shutdown, pressure decay, or another strategy. Fuel level, ambient temperature, coolant temperature, soak time, battery voltage, and driving conditions can determine whether the test runs.

The cap and filler neck should be inspected but not treated as automatic causes. Check the cap seal for damage, swelling, incorrect application, or contamination and inspect the filler-neck sealing surface for rust, dents, or distortion.

Purge and vent valves must be tested electrically and mechanically. A valve can click yet leak, stick, or have restricted flow. Commanded tests combined with fuel-tank pressure data reveal whether the tank is being evacuated, sealed, or vented as expected.

Pressure-sensor plausibility is central. The reading should be believable at atmospheric conditions and move smoothly during controlled vacuum or pressure. Signal direction and scaling vary, so service information controls interpretation.

Smoke testing must use approved low pressure. Seal the vent path and inspect the cap, filler neck, hoses, canister, tank-module seal, pump, valves, rollover devices, and tank shell. Very small leaks may require time, isolation, flow measurement, or decay testing.

A saturated canister can restrict venting and create odor or purge faults. Repeated topping off and liquid fuel in vapor lines must be corrected before replacement.

Verification requires correct valve operation, stable pressure data, no visible smoke leak, acceptable decay or pump results, no pending code, and completed EVAP readiness.