Evaporative emission system leak detected — gross leak or no flow
The controller detected a large sealing failure or an expected flow/pressure change that did not occur during the evaporative-system test.
Conditions that can produce P0455
These are diagnostic branches, not a ranked parts list. Prevalence and testing order depend on the exact vehicle and failure scene.
- Missing, loose, or non-sealing cap
- Disconnected or split vapor hose
- Vent or purge valve stuck open
- Damaged canister, filler neck, tank, or seal
- Leak-detection hardware or pressure-sensor fault
What to inspect next
- Do not operate around fuel vapor, sparks, or hot surfaces
- Perform a complete visual and cap/seal check
- Verify valve sealing and routing
- Use approved smoke pressure and protect the system from overpressure
Evidence that strengthens the answer
Verify the repair
Preserve the pre-repair record, document exactly what changed, then repeat the relevant operating condition safely. Confirm no current or pending fault returns, review permanent-code and readiness state where applicable, and state which tests or modules remained unavailable.
This page explains a commonly standardized code at a general level. Confirm the exact definition, module, status, test conditions, thresholds, wiring, and service process for the vehicle application using current official information.