P0455 Code – EVAP System Large Leak Detected | Meaning, Causes, Symptoms & Fix

The P0455 diagnostic trouble code indicates that the vehicle’s EVAP (Evaporative Emission Control System) has detected a large leak.

In simple terms, fuel vapors are escaping from the fuel system instead of being contained and recycled.

When P0455 appears, the Check Engine Light will illuminate.
Most vehicles continue to drive normally, but emissions will increase and repairs are recommended.

P0455 is one of the most frequently searched EVAP-related OBD2 trouble codes.

What Does P0455 Mean?

The code P0455 stands for:

Evaporative Emission System Leak Detected (Large Leak)

The EVAP system prevents fuel vapors from escaping into the atmosphere.

Main EVAP components:

• Gas cap

• EVAP hoses

• Charcoal canister

• Purge valve

• Vent valve

• Fuel tank seals

If the system detects a major pressure loss, P0455 is triggered.

Quick Overview

Symptoms of P0455

Common symptoms include:

• Check Engine Light ON

• Fuel smell near vehicle

• Failed emissions test

• Slight decrease in fuel economy

• Usually no drivability problems

Many drivers notice only the warning light.

Why the EVAP System Matters

The EVAP system stores fuel vapors inside a charcoal canister and sends them back into the engine to burn.

Without EVAP control:

• fuel vapors escape

• emissions increase

• fuel efficiency decreases

Environmental regulations require this system to work properly.

Most Common Causes of P0455

1️⃣ Loose or Missing Gas Cap (MOST COMMON)

This is the #1 cause of P0455.

Always:

• tighten until it clicks

• check rubber seal for cracks

Sometimes simply tightening the cap clears the code after several drive cycles.

2️⃣ Broken EVAP Hose

Large leaks usually come from:

• disconnected hoses

• cracked plastic lines

• damaged rubber tubing

3️⃣ Faulty Purge Valve

A purge valve stuck open can cause pressure imbalance.

4️⃣ Damaged Vent Valve

If the vent valve cannot seal properly, the system fails leak testing.

5️⃣ Charcoal Canister Damage

Physical damage or saturation may cause major leaks.

Professional Diagnosis Procedure

Step 1 — Check Gas Cap

Inspect seal and tighten correctly.

Step 2 — Perform Smoke Test (Best Method)

Smoke machines help locate leaks quickly.

Step 3 — Inspect EVAP Lines

Check for disconnected or damaged hoses.

Step 4 — Test Purge & Vent Valves

Use diagnostic tool or vacuum tester.

Can You Drive With P0455?

Yes — usually the car will drive normally.

However:

• emissions increase

• fuel vapors escape

• vehicle may fail inspection

Repairs are recommended but not urgent.

Repair Cost for P0455

Vehicles Commonly Affected

P0455 is frequently seen on:

• Dodge

• Jeep

• Chrysler

• Chevrolet

• Ford

• Toyota

• Nissan

Especially older high-mileage vehicles.

Advanced Technical Insight

During self-testing, the ECM seals the EVAP system and checks pressure loss.

If pressure drops too quickly → large leak (P0455).

Small leaks usually trigger:

• P0442 (small leak)

• P0456 (very small leak)

Large leaks almost always indicate a physical opening in the system.

FAQ

Is P0455 serious?

Usually not urgent, but emissions compliance is affected.

Can a loose gas cap cause P0455?

Yes — it is the most common cause.

Will P0455 clear itself?

If the leak is fixed, the code may clear after several drive cycles.

Can I pass emissions testing with P0455?

No, most inspections will fail.

Final Thoughts

The P0455 code indicates a large leak in the EVAP system.

In many cases, the issue is simple — such as a loose gas cap or damaged hose.

Proper diagnosis using a smoke test ensures quick and accurate repairs.

Fixing the issue prevents emissions problems and keeps your vehicle compliant.