P0440: Evaporative Emission System
P0440 means the engine computer found a problem in the evaporative emission control system, which keeps fuel vapors from escaping the gas tank. The most common fix is a loose or damaged gas cap, but leaking EVAP hoses, the purge valve, or the vent valve can also be the cause; typical repairs run about $20 to $350.
- Severity
- Low
- Can I drive?
- Drive with caution
- DIY?
- Possible with some experience
- Repair cost range
- $20 – $450
Get the answer for your exact car
Add your car and a few details. DashClue asks up to 3 questions, then tells you the most likely cause and what it should cost.
FreeNo card neededAnswer in about 2 minutes
What does P0440 mean?
The EVAP system stores fuel vapors from the gas tank and routes them into the engine to be burned instead of vented into the air. Code P0440 sets when the computer sees a leak, blockage, or other fault in that system, but it does not point to one exact part. A loose gas cap is the simplest cause, but cracked hoses, a stuck purge valve, a stuck vent valve, or a leaking charcoal canister can all trigger it. Many cars still drive normally with this code, but the check engine light stays on until the fault is fixed.
Common symptoms
- Check engine light on
- Gas smell around the car
- Hard start after refueling
- Slight drop in fuel economy
- Failed emissions test
- Usually no drivability change
Causes, fixes and costs
P0440: Evaporative Emission System
General guide for most cars. Your car may differ.
P0440 usually will not leave you stranded, but it can let fuel vapors escape and may cause an emissions test failure. Stop driving and get it checked right away if you smell raw fuel strongly, see fuel leaking, or the car starts running badly.
Most likely causes
- 1
Loose, missing, or damaged gas capHigh
This is the most common cause when the light comes on after refueling or the only symptom is the check engine light. A damaged cap seal or cap that will not click tight can set P0440.
Quick check: Remove the cap, inspect the seal for cracks, reinstall it firmly, and see whether it clicks tight. If the cap looks worn or damaged, replace it.
- 2
Cracked or disconnected EVAP hoseMedium
A vacuum leak in an EVAP line can set P0440, especially if there is a fuel smell or the code returns after a gas cap check. Heat and age commonly split plastic or rubber hoses.
Quick check: Look under the hood and near the charcoal canister for cracked, loose, or missing hoses.
- 3
Faulty purge valveMedium
A purge valve that sticks open or does not seal can cause vapor flow problems and may lead to hard starting after refueling or an intermittent check engine light. Some cars also show rough idle if the valve leaks badly.
Quick check: With the engine off, the purge valve should not pass air when closed. A shop can test it with a scan tool or hand vacuum pump.
- 4
Faulty vent valve or charcoal canisterLow
If the vent valve sticks closed or the canister is cracked, the system may not hold or release vapor correctly and the code can return after a fuel fill-up or EVAP test. These faults are more likely when the gas cap and hoses are good.
Quick check: Inspect the canister for damage or fuel saturation and have the vent valve commanded open and closed during a smoke test.
Can you fix it yourself?
Possible with some experience
Difficulty: Moderate. A loose or bad gas cap is easy to handle at home, but most other EVAP diagnoses need a smoke machine or scan tool. If the code comes back after a new cap, ask the mechanic to smoke-test the EVAP system and check the purge and vent valves.
Show the stepsHide the steps
- Tighten or replace the gas cap
- Clear the code and drive normally for a few days
- Check for a fuel smell or obvious cracked hoses
- Inspect EVAP hoses and the canister area for damage
- If the light returns, have the system smoke-tested
- Test or replace the purge or vent valve as needed
Estimated repair cost
$20 – $60
Replace gas cap: parts and labor
- Replace EVAP hose or connector$80 – $200
- Replace purge valve$120 – $280
- Replace vent valve or charcoal canister$180 – $450
- Smoke test and diagnosis$100 – $180
Prices vary by vehicle, parts access, and local labor rates.
Frequently asked questions
Can I drive with code P0440?
Usually yes, as long as the car runs normally and there is no strong fuel smell or fuel leak. It is still a good idea to fix it soon because it can fail an emissions test and the problem may get worse.
Will P0440 clear itself?
Sometimes the light may turn off if the fault was temporary, but the code often comes back if the leak or valve problem is still there. Clearing the code without fixing the cause usually does not solve it.
Is the gas cap really the most common fix?
Yes, on many vehicles a loose, damaged, or missing gas cap is the first thing to check. If a new cap or properly tightened cap does not fix it, the next step is usually an EVAP leak test.
How much does it cost to fix P0440?
A simple gas cap fix can cost under $60, while EVAP hose, valve, or canister repairs usually run about $120 to $450. Diagnosis alone often costs around $100 to $180.
Will P0440 cause a failed inspection?
Yes, in many states an active check engine light or stored emissions code will fail inspection. The EVAP monitor may also not run until the problem is repaired.
Related codes
Related problems
This guide covers most cars and is general advice, not an inspection. Prices are typical US independent-shop ranges and vary by region, car and shop. If your brakes, steering or a warning light feel unsafe, stop driving and contact a mechanic.