P0456 — EVAP system very small leak detected
A tiny EVAP leak — harder to find than a large leak, and easy to overspend on if the shop skips a smoke test.
What it means in plain English
P0456 is a very small EVAP leak. Same family as P0455 / P0442, but the threshold is tighter. Pinpointing often needs a smoke machine and patience; parts-guessing gets expensive.
Common causes
- Marginal gas-cap seal
- Hairline crack in EVAP hose or canister
- Purge/vent valve not sealing fully
What you can safely check
- Reseat/replace a worn gas cap first if the seal is cracked.
- Keep notes of fuel fill-ups (cap left loose overnight is a classic).
Pull the code yourself (disclosed)
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A reusable Bluetooth OBD-II scanner lets you read the code and freeze-frame data before authorizing “mystery” diagnostics. One option: BlueDriver Bluetooth Pro OBD-II scan tool (BlueDriver/Levanta affiliate). Any capable OBD-II reader is fine — this is not required to use Fair Auto Shops.
When to go to a shop
Expect a smoke test. Be wary of estimates that jump to a full canister without leak location documented — second opinion if needed.
Typical related repair costs (U.S. national averages)
These are related repairs shops may find after diagnosis — not a guaranteed bill for every P0456. Ranges exclude taxes, fees, diagnostics, and your location.
- $138–$150 national average for gas cap replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $24–$36; parts about $114.
- $210–$251 national average for purge valve replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $65–$95; parts $146–$156.
Very small leaks can still be a cheap seal — or a buried hose. Price follows diagnosis.
Related cost guides: Gas Cap · Purge Valve
Questions to ask before you authorize work
Use questions before you authorize a repair and how to read a repair estimate. Watch for patterns in spotting upselling.
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FAQ
What should I do first with a P0456 code?
Photograph all codes, note symptoms and whether the light is flashing, avoid clearing data until a shop sees it, then use an independent shop with a clear diagnostic plan.
More check-engine codes
P0420 · P0430 · P0300 · P0301 · P0171 · P0174 · P0455 · P0442 · P0446 · P0128 · P0401 · P0133 · P0113 · P0506 · P0507 · P0700 · P0741 · P0011 · P0325 · P0340 · P0335 · P0101 · P0299 · P0135 · P0440 · P0441 · P0010 · P0500 · P0121
Hub: How to read a check-engine code · Repair cost guides · Affiliate disclosure