What does code P0456 mean on a GMC and is it safe to drive?
P0456: Evaporative Emission System Leak Detected (Very Small Leak). Here's what it means on your GMC, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
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What this code means
The EVAP system has detected a very small leak—often smaller than P0442. Commonly caused by a loose fuel cap or hairline crack in a hose.
Common causes for your GMC
- Loose or worn gas cap seal
- Hairline crack in EVAP hoses
- Minor leak at purge or vent valve fittings
Symptoms
- Check Engine Light only
- Usually no noticeable driving symptoms
Typical fixes
- Inspect and replace gas cap if seal is hardened or cracked
- Smoke-test EVAP system to locate tiny leaks
- Repair or replace leaking hoses and fittings
Repair cost range
For a GMC, repairs for P0456 often fall between $25 and $350, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on GMC
GMC P0456 small EVAP leak is most commonly the gas cap. On Sierra trucks, the filler neck grommet can shrink with age allowing a small vapor leak. Replace the gas cap first; if P0456 returns, smoke test the filler neck connection.
Most commonly affected models
Sierra 2007–2014Terrain 2010–2017Acadia 2007–2016