Is P0440 the same as P0455?

They're related but not identical. P0440 is a general EVAP malfunction code, most common on older vehicles. P0455 specifically indicates a large leak. On newer vehicles, P0440 is often replaced by more specific codes.

Should I keep driving with P0440?

Yes. P0440 does not affect how the car runs or its safety. Address the underlying cause within a few weeks, especially if an emissions inspection is coming up.

Will it pass emissions?

No. EVAP codes cause OBD-II emissions inspections to fail. The code must be resolved and the EVAP readiness monitor must complete before the vehicle can pass.

What's the first thing to try?

Tighten the gas cap until it clicks, or replace it with a new one if it looks worn. Drive three to five complete drive cycles and rescan. If the code returns, move on to a visual inspection and smoke test.

OBD-II trouble code

P0440: Evaporative Emission Control System Malfunction

A general code indicating a problem with the evaporative emission (EVAP) system. Most often a loose gas cap, a cracked hose, or a faulty purge or vent valve. The car drives normally but will fail an emissions test.

Quick facts

System: Powertrain
Category: Emissions / EVAP
Severity: Low severity
Drivable: Usually safe to drive short-term
Repair cost range: $20 – $600
DIY difficulty: Beginner DIY

What does P0440 mean?

P0440 is an umbrella code for an EVAP system malfunction. The evaporative emission system collects fuel vapors from the gas tank, stores them in a charcoal canister, and routes them into the engine intake to be burned during normal driving — preventing raw fuel vapors from escaping to the atmosphere.

On older vehicles (roughly model years 1996 to early 2000s), the engine control module (ECM) often sets P0440 as a generic indicator without narrowing down the specific failure mode. On newer vehicles, the ECM is more sophisticated and typically sets a more specific code like P0442 (small leak), P0455 (large leak), P0446 (vent valve circuit), or P0457 (gas cap loose) instead of — or alongside — P0440.

Because P0440 is intentionally vague, the diagnosis starts with the cheapest and most common causes: gas cap, visible hose damage, and a basic smoke test. The repair is rarely expensive and never affects driveability — but the code does cause emissions test failures.

Common causes

Loose, missing, or worn gas cap (a top cause on the older vehicles that throw P0440)
Cracked or disconnected EVAP hose
Failed purge valve stuck open or closed
Failed vent valve stuck open or closed
Cracked charcoal canister
Damaged fuel filler neck
Disconnected EVAP system connector or wiring fault

Symptoms

Check engine light is on
Occasional faint fuel odor
Failed emissions inspection
No driveability impact

Diagnostic steps

1.Scan the vehicle and check for additional EVAP codes (P0442, P0446, P0455, P0457). P0440 alone is generic; companion codes narrow the diagnosis.
2.Inspect and re-seat the gas cap. Drive 3 to 5 full cycles and rescan.
3.Visually inspect every EVAP hose and connector accessible without disassembly.
4.Smoke-test the EVAP system.
5.Use a scan tool to functionally test the purge and vent valves.

Repair cost

$20 – $600

A gas cap is $15 to $40 and fixes a meaningful share of P0440 cases on older vehicles. EVAP hose or valve repairs run $100 to $400. Charcoal canister replacement is $300 to $600. A diagnostic smoke test is $50 to $150.

Estimate your repair

Run the numbers for your vehicle

Open the Repair Cost Estimator with evap system repair preselected. Adjust labor rate and vehicle category to fit your situation.

Estimate your repair cost

DIY vs shop

This is a beginner-friendly repair. Common hand tools, a free afternoon, and a willingness to follow a procedure are usually enough. The risk of causing a bigger problem is low if you read up on your specific vehicle first.

Related codes

P0442 P0446 P0455 P0456 P0457