Emissions code
P0455: Large fuel vapor leak
The fuel-vapor system is sealed so gas fumes cannot escape, and the computer tests it by pulling a light vacuum or pressure on it. This time the pressure fell away fast, which means a large opening such as a loose or missing gas cap, or a hose that has come off.
- Safe to drive?
- Usually yes, for now
- Most common cause
- Gas cap loose, missing or worn seal
Safe to drive; this does not hurt the engine, though it will fail an emissions inspection.
How this range is built
| Part of the job | Low | High |
|---|---|---|
| Parts | $8 | $40 |
| Labor: 0 to 0.3 hours × $125 to $175 an hour | $0 | $53 |
| Fees: shop supplies, disposal, diagnostics | $0 | $10 |
| Total, rounded | $5 | $110 |
The hourly rate is the BLS Occupational Employment and Wage Statistics, May 2025 average pay for this trade in Boston, $31.54 an hour, times 4 to 5.5 to cover what a shop bills (overhead, tools, insurance, profit). Parts are a band from budget aftermarket to the manufacturer part. Full method.
Not a repair shop, estimates only. Typical range, estimate. Not a quote. Your car, parts and shop change the number.
This is the range for the most common fix, gas cap replacement. Which repair your car needs depends on a proper diagnosis.
What you may notice
- Check-engine light on
- Fuel smell near the car
- Hard to fill the tank (rare)
Common causes, most likely first
- Gas cap loose, missing or worn seal
- Cracked EVAP hose or filler neck
- Stuck-open purge or vent valve
- Damaged charcoal canister
- Leak at the fuel tank seal
Check this first
Remove and re-tighten the gas cap until it clicks, then drive a few days. If the light stays, ask for a smoke test of the vapor system.
Other repairs that sometimes fix P0455
| Repair | Typical range, Boston |
|---|---|
| EVAP vent valve replacement | $120 to $360 |
| EVAP purge valve replacement | $85 to $260 |
| Diagnostic scan (check engine light) | $60 to $290 |
Before you pay
- Ask the shop what test showed this part is the cause, not just that the code appeared.
- Ask for parts and labor listed separately, and for the hours.
- Ask for a written OK before any extra work. Massachusetts rules require written authorization before repairs.
Got a quote already? Check it against the range. Want to see if your car has a recall tied to this problem? Check recalls by VIN.
Need to read a code yourself? OBD-II scanners on eBay (affiliate link, disclosure).
P0455 questions
Can a loose gas cap really do this?
Yes. A cap that is loose, cracked or missing its seal is the most common reason for a large-leak code. A new cap costs little, so it is a fair first try before paying for any testing.
How long until the light goes out after I fix it?
The light often goes out after a few days of normal driving, because the car has to repeat its self-test several times. A shop can clear it sooner, but if the leak is still there it will come back.
Is a fuel vapor leak dangerous?
Not usually. The fumes are harmful to air quality but the system is not under pressure like a gas line. If you smell strong fuel around the car or see a drip, have it looked at sooner.
How much does it cost to fix P0455?
The most common fix, gas cap replacement, has a typical range of $5 to $110 in Boston. It is an estimate built from parts prices and local labor wages, not a quote. Your car and shop change it.
P0455 repair cost by city
Related codes
- P0442: Small fuel vapor leak
- P0456: Very small fuel vapor leak
- P0457: Fuel vapor leak, gas cap may be loose
- P0446: Fuel vapor vent circuit problem
More emissions codes
Code meaning written in our own words. Some codes mean different things on different makes, so check your scan tool or manual. Not a repair shop, estimates only.