Freeze Frame
OBD-II trouble code

P0455

Evaporative Emission System Leak Detected (Large Leak)

Severity Moderate Driving See conditions below System Evaporative emissions Applies to OBD-II gasoline vehicles with an evaporative-emissions leak monitor; exact coverage and hardware vary.

Published · Reviewed and updated

In plain English: The EVAP monitor detected a large leak or could not achieve its required pressure response. Check the cap or capless inlet, hoses and valve operation before replacing parts.

A short trip may be possible if the vehicle runs normally and there is no fuel odor or leakage. Arrange prompt diagnosis. Stop for strong fuel odor, visible fuel, repeated stalling, severe rough running or a flashing check-engine light. Keep ignition sources away from suspected fuel leaks.

A diagnostic starting point: Fuel cap, capless inlet or filler-neck sealing fault. Start by asking: Does the cap or capless inlet pass its specified inspection? Illustrative parts budgets span $10–$480 USD, with diagnosis, labor and taxes extra.

Quick answers about P0455

What does P0455 mean?
The EVAP monitor detected a large leak or could not achieve its required pressure response. Check the cap or capless inlet, hoses and valve operation before replacing parts.
What should I check first for P0455?
One starting point is Fuel cap, capless inlet or filler-neck sealing fault. Check the fitted design and its approved inspection procedure. A cap is an accessible check where fitted, not a universal repair. The code alone does not identify a failed part; follow the procedure for your vehicle.
Can I drive with P0455?
A short trip may be possible if the vehicle runs normally and there is no fuel odor or leakage. Arrange prompt diagnosis. Stop for strong fuel odor, visible fuel, repeated stalling, severe rough running or a flashing check-engine light. Keep ignition sources away from suspected fuel leaks.
How much does it cost to fix P0455?
Illustrative parts budgets in this guide span $10–$480 USD. Diagnosis, labor and taxes are extra. A repair may involve an inlet seal, hose, circuit, valve or larger assembly. These examples cannot price an untested fault; obtain an itemized estimate after diagnosis.
How do I diagnose P0455?
Start with: Does the cap or capless inlet pass its specified inspection? With ignition off and no suspected liquid fuel leak, inspect the fitted cap, seal and filler area using the owner or service manual. Refit a cap as specified; click counts are not universal. For a capless system use its approved procedure and tools. Save codes before clearing and confirm the monitor after repair.

Watch the P0455 videos

Full diagnostic video · 8:50 YouTube Short · 1:06

Correction, October 15, 2026: The written guide now uses safer, vehicle-specific EVAP checks. The older videos may contain earlier advice. Do not mouth-test fuel-vapor parts; use approved EVAP equipment and the exact vehicle procedure. Driving guidance and monitor thresholds below supersede the older wording.

Full walkthrough — 8:50. Watch on YouTube

What P0455 actually means

The charcoal canister stores fuel vapor and the purge system meters it into the engine. The vent path normally allows controlled air exchange and can be isolated for particular tests. The required valve states depend on the system; the vapor system is not permanently sealed from atmosphere.

Manufacturers use different vacuum, pressure, pump or switch-based checks. P0455 can result when the expected test pressure cannot be reached, including from a large opening or inadequate purge flow on some systems. Follow the exact monitor procedure and validate the pressure signal. No universal hole diameter, pressure trace or time limit identifies P0455 on every vehicle.

Fuel tank Intake Charcoal canister — traps the vapour Purge valve Vent valve ← to atmosphere Cap or capless inlet Check the fitted design; no universal failure rate
Schematic illustration; the vehicle's layout may differ. A large-leak or inadequate-pressure-response result that needs testing.

Symptoms

Possible causes and what to check

This is a practical diagnostic order, not measured failure rates. Follow the tests and priorities specified for your vehicle; a code alone does not identify a failed part.

1 Fuel cap, capless inlet or filler-neck sealing fault
Check the fitted design and its approved inspection procedure. A cap is an accessible check where fitted, not a universal repair.
2 Cracked, disconnected or restricted EVAP hose
Inspect routing, connections and damage. A blockage can prevent the expected test response on some systems.
3 Purge valve or purge-flow problem
Verify sealing and commanded flow with the specified method. A lack of flow can resemble a large leak in some monitors.
4 Vent valve, circuit or air-path problem
Verify electrical control and the required mechanical state; a click alone does not prove sealing or flow.
5 Canister, tank or vapor-line leak
Isolate the leak with approved equipment before replacing an assembly.
6 Pressure feedback or other test-condition problem
Check signal plausibility, other valves, fuel level and enabling conditions in the vehicle procedure.

Illustrative EVAP test pressure responses

Illustrative graph, not a recording from your vehicle or a universal service limit. Confirm the test conditions, units and acceptance criteria in the applicable service procedure.

These invented curves illustrate possible pressure responses, not universal code thresholds.

These invented curves show a hypothetical vacuum test. Negative gauge pressure means vacuum here. Valve states, sensor location and test timing must match the vehicle procedure. The plotted values are not directions to apply vacuum and do not measure a physical leak diameter.

-12.0 -9.2 -6.4 -3.6 -0.8 2.0 0 24 48 72 96 120 Gauge pressure (inches H2O; illustrative) Seconds in an illustrative test Vacuum retained - illustrative Vacuum decays - illustrative Weak vacuum response - illustrative
Weak vacuum response: check leaks, flow and feedback. Use the vehicle monitor to classify the fault.

The green example develops vacuum and changes relatively slowly after isolation. A repair is verified only when the specified functional checks and completed monitor pass, not simply because a trace resembles this drawing.

The red example develops little vacuum. A large opening can cause this, but inadequate purge flow, an incorrect valve state, restricted plumbing or misleading pressure feedback may also affect the result. The shape does not identify the failed part.

The middle example loses vacuum more gradually. Actual leak classifications depend on the manufacturer test, vapor generation and conditions. Do not assign P0442 or P0455 from this generic curve alone.

How to diagnose it, in order

  1. Does the cap or capless inlet pass its specified inspection?
    With ignition off and no suspected liquid fuel leak, inspect the fitted cap, seal and filler area using the owner or service manual. Refit a cap as specified; click counts are not universal. For a capless system use its approved procedure and tools. Save codes before clearing and confirm the monitor after repair.
    Yes → go to step 2
    No → Repair the demonstrated inlet or cap defect, then verify
  2. Are all EVAP hoses intact from the tank to the canister to the engine?
    With the vehicle safely supported, inspect accessible lines for splits, disconnected fittings, pinching and recent repair damage. Repair demonstrated defects and retest; visible damage may not be the only fault.
    Yes → go to step 3
    No → Repair or replace the damaged hose
  3. Does purge sealing and commanded flow pass the specified test?
    Identify the required purge-valve state from service information. Use an approved hand pump, gauge or flow tester within the specified limits to check sealing and flow. Never blow or suck through fuel-vapor components by mouth. Check electrical control before condemning a valve.
    Yes → go to step 4
    No → Repair the proven purge-flow, valve or control fault
  4. Does the vent system reach and hold the required test state?
    Use the correct diagram and suitable scan tool to verify the commanded vent state, electrical control and actual sealing or flow. Resting states and integrated valve designs vary. Hearing a click does not prove that the test space is sealed.
    Yes → go to step 5
    No → Repair the proven vent, circuit or path fault
  5. Do approved leak and pressure-response tests isolate the fault?
    Use approved low-pressure EVAP equipment with the engine off, the specified inert gas and no ignition sources nearby. Follow the vehicle connection and isolation procedure. Check for leaks, but if none are found also investigate purge flow, restrictions, valve states and pressure feedback. Do not apply unrestricted shop air.
    Yes → Repair the demonstrated defect and verify the completed monitor
    No → Continue manufacturer tests for flow, valve state and signal validity

Repair the demonstrated defect, repeat the failed test and confirm the relevant monitor completes successfully. Clearing the light alone does not verify a repair.

What you need to do this yourself

Some links may be affiliate links. They cost you nothing extra and do not change which tools are recommended — the diagnostic order on this site is the same either way.

Illustrative repair budgets

Rough US planning examples only, not measured averages or shop quotes. Parts and labor are separate; diagnosis, access, taxes and additional repairs can change the total.

Illustrative budgets in USD; labor time is shown separately
RepairParts (USD)Labor time
Fuel cap
Only applies where a replaceable cap is fitted and its defect is demonstrated.
 $10–$35 0.1 h
EVAP hose or line
Cheap unless the split section is buried above the tank.
 $10–$45 0.7 h
Purge valve
Usually under the bonnet and straightforward to reach.
 $25–$130 0.7 h
Vent valve
Often mounted near the tank, so labour depends on access and rust.
 $30–$150 1.0 h
Charcoal canister
Replace only after the defect is isolated; access and integrated hardware affect cost.
 $120–$480 1.5 h

A repair may involve an inlet seal, hose, circuit, valve or larger assembly. These examples cannot price an untested fault; obtain an itemized estimate after diagnosis.

P0455 video summary · 1:06

A brief introduction to the code and a diagnostic starting point. Use the full guide and vehicle-specific service information for the complete procedure.

Watch this Short on YouTube

Written diagnostic walkthrough

Current written guidance organized by topic. This text may include corrections made after a video was published and is not a verbatim transcript of the archived video.

Meaning and driving guidance

Code P0455. Evaporative Emission System Leak Detected (Large Leak).

In plain English: the EVAP monitor detected a large leak or could not achieve its required pressure response. Check the cap or capless inlet, hoses and valve operation before replacing parts.

A short trip may be possible if the vehicle runs normally and there is no fuel odor or leakage. Arrange prompt diagnosis. Stop for strong fuel odor, visible fuel, repeated stalling, severe rough running or a flashing check-engine light. Keep ignition sources away from suspected fuel leaks.

How it is measured

Here's what your engine computer is actually measuring.

The charcoal canister stores fuel vapor and the purge system meters it into the engine. The vent path normally allows controlled air exchange and can be isolated for particular tests. The required valve states depend on the system; the vapor system is not permanently sealed from atmosphere.

Manufacturers use different vacuum, pressure, pump or switch-based checks. P0455 can result when the expected test pressure cannot be reached, including from a large opening or inadequate purge flow on some systems. Follow the exact monitor procedure and validate the pressure signal. No universal hole diameter, pressure trace or time limit identifies P0455 on every vehicle.

So the code is not a part failure report. It's a performance measurement that came back under spec.

Symptoms

What you'll usually notice, beyond the light itself.

Check-engine light, sometimes without a change in running. Save codes and freeze-frame information before clearing them.

Emissions-test or readiness concerns. A stored fault or incomplete monitor may affect an inspection; requirements depend on the jurisdiction.

Fuel odor or visible leakage. These need prompt attention. Strong odor or visible fuel is a reason to stop, even if the vehicle still runs normally.

The fault appears after refueling or recent repairs. Inspect the correct cap or capless inlet and disturbed hoses. Timing is a useful clue, not proof of the cause.

Possible causes

Here is a practical order for checking the possible causes. These are diagnostic priorities, not measured failure rates.

Check 1: Fuel cap, capless inlet or filler-neck sealing fault. Check the fitted design and its approved inspection procedure. A cap is an accessible check where fitted, not a universal repair.

Check 2: Cracked, disconnected or restricted EVAP hose. Inspect routing, connections and damage. A blockage can prevent the expected test response on some systems.

Check 3: Purge valve or purge-flow problem. Verify sealing and commanded flow with the specified method. A lack of flow can resemble a large leak in some monitors.

Check 4: Vent valve, circuit or air-path problem. Verify electrical control and the required mechanical state; a click alone does not prove sealing or flow.

Check 5: Canister, tank or vapor-line leak. Isolate the leak with approved equipment before replacing an assembly.

Check 6: Pressure feedback or other test-condition problem. Check signal plausibility, other valves, fuel level and enabling conditions in the vehicle procedure.

Use the test results to choose the repair. A position in this list does not prove that a part has failed.

Illustrative diagnostic pattern

These invented curves illustrate possible pressure responses, not universal code thresholds.

These invented curves show a hypothetical vacuum test. Negative gauge pressure means vacuum here. Valve states, sensor location and test timing must match the vehicle procedure. The plotted values are not directions to apply vacuum and do not measure a physical leak diameter.

The green example develops vacuum and changes relatively slowly after isolation. A repair is verified only when the specified functional checks and completed monitor pass, not simply because a trace resembles this drawing.

The red example develops little vacuum. A large opening can cause this, but inadequate purge flow, an incorrect valve state, restricted plumbing or misleading pressure feedback may also affect the result. The shape does not identify the failed part.

The middle example loses vacuum more gradually. Actual leak classifications depend on the manufacturer test, vapor generation and conditions. Do not assign P0442 or P0455 from this generic curve alone.

Diagnostic steps

Save the diagnostic record and follow the exact vehicle procedure. These are diagnostic priorities, not measured failure frequencies.

Step 1. Does the cap or capless inlet pass its specified inspection? With ignition off and no suspected liquid fuel leak, inspect the fitted cap, seal and filler area using the owner or service manual. Refit a cap as specified; click counts are not universal. For a capless system use its approved procedure and tools. Save codes before clearing and confirm the monitor after repair.

Step 2. Are all EVAP hoses intact from the tank to the canister to the engine? With the vehicle safely supported, inspect accessible lines for splits, disconnected fittings, pinching and recent repair damage. Repair demonstrated defects and retest; visible damage may not be the only fault.

Step 3. Does purge sealing and commanded flow pass the specified test? Identify the required purge-valve state from service information. Use an approved hand pump, gauge or flow tester within the specified limits to check sealing and flow. Never blow or suck through fuel-vapor components by mouth. Check electrical control before condemning a valve.

Step 4. Does the vent system reach and hold the required test state? Use the correct diagram and suitable scan tool to verify the commanded vent state, electrical control and actual sealing or flow. Resting states and integrated valve designs vary. Hearing a click does not prove that the test space is sealed.

Step 5. Do approved leak and pressure-response tests isolate the fault? Use approved low-pressure EVAP equipment with the engine off, the specified inert gas and no ignition sources nearby. Follow the vehicle connection and isolation procedure. Check for leaks, but if none are found also investigate purge flow, restrictions, valve states and pressure feedback. Do not apply unrestricted shop air.

Repair the demonstrated defect, repeat the failed test and confirm the relevant monitor completes successfully. Clearing the light alone does not verify a repair.

Illustrative repair budgets

Rough US planning examples only, not measured averages or shop quotes. Parts and labor are separate; diagnosis, access, taxes and additional repairs can change the total.

Fuel cap: 10 to 35 dollars in parts, plus about 0.1 hours of labor. Only applies where a replaceable cap is fitted and its defect is demonstrated.

EVAP hose or line: 10 to 45 dollars in parts, plus about 0.7 hours of labor. Cheap unless the split section is buried above the tank.

Purge valve: 25 to 130 dollars in parts, plus about 0.7 hours of labor. Usually under the bonnet and straightforward to reach.

Vent valve: 30 to 150 dollars in parts, plus about 1.0 hours of labor. Often mounted near the tank, so labour depends on access and rust.

Charcoal canister: 120 to 480 dollars in parts, plus about 1.5 hours of labor. Replace only after the defect is isolated; access and integrated hardware affect cost.

A repair may involve an inlet seal, hose, circuit, valve or larger assembly. These examples cannot price an untested fault; obtain an itemized estimate after diagnosis.

Sources and application limits

These manufacturer documents and technical references support the discussion. A bulletin may apply only to its listed models, engines and production dates; confirm coverage before applying it.

P0442 P0456 P0446 P0440