The most common causes are: Fuel cap not fully tightened or with a slightly worn seal; Tiny crack in an EVAP hose; Slightly leaking purge or vent valve; Degraded O-ring at a connection point; Hairline crack in the charcoal canister.

How much does it cost to fix P0456?

Typical repairs range from $15–$60 for replace fuel cap up to $250–$700 for replace charcoal canister. Costs vary by vehicle and region.

P0456powertrain

P0456 – Evaporative Emissions System - Small Leak Detected

What does P0456 mean?

The EVAP system has detected a very small leak — smaller than what triggers P0442. The system monitors for leaks as small as roughly 0.020 inches, so this code can be set by a leak far too small to see.

What causes P0456?

Listed from most to least common:

1Fuel cap not fully tightened or with a slightly worn seal
2Tiny crack in an EVAP hose
3Slightly leaking purge or vent valve
4Degraded O-ring at a connection point
5Hairline crack in the charcoal canister
6Leaking fuel tank seal or sending unit gasket

Code breakdown

SystemP — Powertrain

TypeGeneric (standardized SAE / OBD-II code — same meaning across most manufacturers)

SubsystemAuxiliary emission controls

Common symptoms

Check engine light on
Completely normal drivability
Failed emissions test

How to diagnose

1Tighten the fuel cap fully until it clicks, clear the code, and drive several cycles.
2Replace the fuel cap if the seal shows any wear — it is the cheapest possible fix.
3Smoke-test the EVAP system. For leaks this small, smoke testing is effectively the only practical method.
4Pay particular attention to the fuel sending unit gasket and canister seams during the test.
5Verify purge and vent valves seal completely.

No drivability impact whatsoever, but it will fail emissions testing and can be genuinely difficult to track down.

Common fixes and estimated costs

Repair	Estimated cost
Replace fuel cap	$15–$60
Replace hose or O-ring	$50–$250
Replace purge or vent valve	$100–$350
Replace charcoal canister	$250–$700

Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.

Good to know

The EVAP monitor only runs under specific conditions — often requiring a partially full tank and a cold start after sitting overnight. After a repair, expect several drive cycles before the code clears and monitors reset.

Back to all Powertrain Codes →

This information is provided for general reference only and may vary by manufacturer, model, and year. It is not a substitute for professional diagnosis or repair.