P0455 Large EVAP Leak Detected

What it means

This is the same seal test as P0442, with a worse result. The system could not hold vacuum or pressure at all, so something is open. The simplest cause is also the most common one: a gas cap left loose after a fill-up.

The technical version

The EVAP monitor closes the vent, applies vacuum or pressure and watches tank pressure. P0455 means the system never reached the target, which points to a gross leak, a disconnected hose or a valve stuck open. Some cars show a 'check fuel cap' message before they set a code.

Official name: Evaporative Emission Control System Leak Detected (gross leak).

Symptoms

• Usually none apart from the light.
• A fuel smell, if a hose is off.
• A 'check fuel cap' message on some cars.

Causes, most likely first

How likely is our ranking from repair data and common practice, not a published rate.

What the live data shows

With the system open, purge is commanded but tank pressure does not respond. After you reseat the cap, watch the EVAP readiness monitor over the next few drives. When it shows complete and the code stays away, the leak is fixed.

What to check first, in order

1. Check the gas cap: present, tight, clicks, seal not torn.

   It is the classic cause.

   What the data shows: No reading needed.

   Cost: $138-$150 at a shop (Gas cap replacement, RepairPal)

2. Look for an obviously loose hose near the tank and canister.

   A large leak is often visible.

   What the data shows: No reading needed.

   Cost: free

3. Clear the code and drive a few days.

   The EVAP test needs time to run.

   What the data shows: EVAP readiness changes to complete.

   Cost: no cost if you have a scanner

4. If it returns, have a smoke test done.

   It finds a stuck valve or hidden crack.

   What the data shows: Not a scanner step.

   Cost: $61-$90 at a shop (Emission system diagnosis (shop), RepairPal)

Is it safe to drive?

Drive normally - check soon

Yes. It is a vapor leak, not a fuel leak.

Harmless to drive with. You lose a little fuel to evaporation, may smell fuel, and will fail an emissions test until it is fixed.

Stop driving and get help if

• You see liquid fuel dripping or smell strong fuel inside the car.

What it costs

National averages for the full job at a shop, parts and labor, from RepairPal (updated September 3, 2026). Your price depends on the car and the area. Many of the first checks on this page cost nothing with a scanner. The EVAP purge valve was CarMD's number 6 check engine repair in 2025, at an average of $172. CarMD averages come from a different method (repairs reported by its users), so they can sit below RepairPal's shop estimates.

Sources for the notes: CarMD 2026 Vehicle Health Index (press release, April 22, 2026).

Can I clear it? Will it come back?

Clearing resets the EVAP monitor. It can take several days of normal driving to run again, so do not clear it right before a test.

Will it fail an emissions test?

Yes, while the check engine light is on, most OBD emissions tests fail the car.

Carmaker notes

Service bulletins and warranty extensions that name this code. Ask a dealer to check your VIN.

• Infiniti 2012 and newer

  Infiniti bulletin EC13-015h (November 2020) says a loose fuel filler cap may be the cause of EVAP leak codes. Check the cap first.

  Infiniti EC13-015h via NHTSA static.nhtsa.gov

• GM 2007-2010 Escalade, Avalanche, Suburban 1500, Tahoe, Yukon

  GM bulletin 09-06-04-028D (April 2014) links P0455 and other EVAP codes to water and corrosion at the EVAP vent (CVS) valve.

  GM 09-06-04-028D via NHTSA static.nhtsa.gov

Related codes

Also related, no guide yet: P0456, P0457, P0446.

Questions people ask

Will a gas cap fix P0455?

Often. Check and tighten the cap first. If the code comes back, look for a loose hose or a stuck valve.

How long does P0455 take to clear after tightening the cap?

The light goes out once the EVAP test passes, which can take several days of normal driving.

Is P0455 worse than P0442?

It is a bigger leak, but it is still an emissions fault, and often a cheaper fix.

Sources

1. RepairPal: P0455 code page repairpal.com
2. RepairPal: Emission system diagnosis (shop) (updated September 3, 2026) repairpal.com
3. RepairPal: Gas cap replacement (updated September 3, 2026) repairpal.com
4. RepairPal: EVAP purge valve replacement (updated September 3, 2026) repairpal.com
5. RepairPal: EVAP canister replacement (updated September 3, 2026) repairpal.com
6. CarMD 2026 Vehicle Health Index (press release, April 22, 2026) prnewswire.com
7. Infiniti EC13-015h via NHTSA static.nhtsa.gov
8. GM 09-06-04-028D via NHTSA static.nhtsa.gov
9. Texas DPS emissions testing FAQ dps.texas.gov
10. Arizona myazcar.com: OBD and the check engine light myazcar.com