Emission codes
P0440: evaporative emission system malfunction
Your fuel tank gives off gasoline vapor all the time. The EVAP system traps it in a charcoal canister and burns it in the engine later. P0440 is the general code for a fault the computer found in that system.
P0440: can I drive, and what will the labor cost?
Estimated labor, replace the gas cap
$11 to $22
| Labor time (estimate) | 0.1 to 0.2 h |
| Rate used | $110/h |
| Technician wage, United States (average) | $27.13/h |
| Low: fix when convenient Safe to drive; it is an emissions fault, not a safety one, but the car will not pass an OBD inspection. | |
Labor only: parts and the diagnostic fee are not included. Hours are our estimate for a typical car; book times vary by model. Wage: BLS, May 2025.
P0440 is the generic OBD-II code for "evaporative emission system malfunction". The system is a sealed loop: the tank, its filler neck and cap, vapor lines, a charcoal canister that adsorbs the vapor, a vent valve that lets the canister breathe fresh air, and a purge valve that lets the engine draw the stored vapor in and burn it. Federal rules require the computer to check that loop for leaks and for working valves, and the rules for model year 2017 and later set the smallest leak to detect at a hole of 0.020 inch (40 CFR 86.1806-17). P0440 is the broad code some makers use when the test fails without a more specific result. The usual causes are a loose, worn or wrong gas cap, a purge or vent valve fault, a cracked hose or filler neck, and a saturated canister. It is an emission fault, not a safety one: safe to drive, but the car fails an OBD inspection.
After the repair: when does the light go off?
Light off by itself after about
2 days
| Fault-free trips needed | 3 |
| Warm-up cycles before the code can be erased | 40 |
| Stored code gone after about | 40 days |
Federal rule for model years up to 2016 (40 CFR 86.1806-05); a misfire or fuel fault must also stay away under similar conditions. Clearing codes with a scanner also resets the readiness monitors an inspection checks.
Codes, rules and labor data checked by Radif Partners · Editorial policy · Method and sources
P0440 at a glance
| Code | P0440 |
| Standard description | Evaporative Emission System Malfunction |
| System | Evaporative emissions (EVAP) |
| Severity | Low: fix when convenient |
| Common symptoms | usually none, fuel smell near the car |
How the car tests itself
Most systems close the vent valve, open the purge valve briefly so that engine vacuum pulls the system below atmospheric pressure, then close everything and watch the tank pressure sensor. If the vacuum fades too quickly, there is a leak; if it never forms, a valve or a large opening is to blame. Other systems use a small pump at the canister instead of engine vacuum. The test runs only in certain conditions, often after a cold soak, with the tank between a quarter and three quarters full, which is why the light can take days to come on or go off.
What to check, cheapest first
- The gas cap: tighten it until it clicks, look at the rubber seal, and replace it if cracked or if it is not the correct cap for the car.
- The filler neck lip, for rust or dents that stop the cap from sealing.
- A smoke test by a shop, which pushes visible vapor into the system and shows the leak.
- Purge and vent valves, which a scanner can command open and closed.
More specific codes point to the size and place of the problem: P0455 for a large leak, P0442 for a small one, P0446 for the vent. After a fix, the light goes off after 3 good trips, and the counter on this page estimates how long that takes.
Likely causes of P0440, in order
| Cause | How often |
|---|---|
| Loose, worn or wrong gas cap | most frequent |
| Purge or vent valve fault | frequent |
| Cracked vapor hose or filler neck | frequent |
| Saturated or cracked charcoal canister | less frequent |
P0440 repairs and labor time
| Repair | Labor (estimate) | At $110/h |
|---|---|---|
| Replace the gas cap | 0.1 to 0.2 h | $11 to $22 |
| EVAP smoke test to find the leak | 0.5 to 1 h | $55 to $110 |
| Replace EVAP purge valve | 0.3 to 1 h | $33 to $110 |