P0440: Evaporative Emission System
The engine computer has found a general problem in the EVAP system, which traps gasoline vapor from the tank so it does not escape into the air.
What P0440 means
The EVAP system catches gasoline vapor that boils off the fuel tank and stores it in a charcoal canister. When the engine is warm and running, a purge valve opens and the engine burns those vapors. A vent valve lets fresh air in or seals the system for testing. Periodically, the engine computer seals the system and checks whether it holds vacuum or pressure. P0440 is a general fault code for this system. RepairPal lists a missing or damaged fuel cap, a damaged filler neck, torn hoses, a split canister, bad vent or purge valves and a leaking tank or sending unit seal as common causes. Most drivers notice nothing besides the light, though some smell fuel. KBB points out that fuel vapor in or around the cabin can be dangerous, so a strong smell deserves quick attention. Shops start with the cap, then run a smoke test that fills the system with visible vapor to show exactly where it escapes.
Common symptoms
- Check engine light on
- Usually no change in how the car drives
- Faint fuel smell near the car or the fuel door
- Failed emissions or readiness test
- Other EVAP codes may appear at the same time
Most common causes
- Missing, loose or damaged gas cap
- Damaged fuel filler neck
- Torn or cracked EVAP hoses
- Split or damaged charcoal canister
- Faulty EVAP vent or purge valve
- Leaking fuel tank or fuel pump seal
What to check yourself first
Check that the gas cap is on tight and clicks, and look at its rubber seal for cracks. Look under the car near the tank for cracked or disconnected EVAP hoses. Clear the code and drive for a few days to see whether it returns.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| EVAP smoke test to find the leak | $61-$90 | A smoke test is the standard way to find EVAP leaks. |
| Replace gas cap (shop price) | $138-$150 | RepairPal lists the gas cap as both a common cause and a common misdiagnosis, so test it before assuming. |
| Replace EVAP purge valve | $210-$251 | If the purge valve fails a vacuum or electrical test. |
| Replace EVAP canister (includes vent valve on many cars) | $558-$643 | When the canister or its vent valve is cracked or stuck. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0455 Evaporative Emission System Leak Detected (large leak)
- P0442 Evaporative Emission System Leak Detected (small leak)
- P0456 Evaporative Emission System Leak Detected (very small leak)
- P0441 Evaporative Emission System Incorrect Purge Flow
- P0446 Evaporative Emission System Vent Control Circuit