P0440: EVAP system fault (general)
EVAP system malfunction
Severity: Monitor
EVAP faults let fuel vapour escape but rarely change how the car drives, and the main risk is a failed emissions test, so it is safe to drive while you arrange a fix.
It gets more serious if:
- Inspect soon: You keep smelling raw fuel around the car, not just right after filling up
- Stop: You see liquid fuel dripping or pooling under the car, or near the filler, tank or canister
P0440 in short
P0440 is a general fault code for the fuel vapour (EVAP) system. It does not say which part failed. Start with the fuel cap, then the purge valve, the hoses and the vent valve. It is generally safe to drive, but stop driving if you see fuel leaking.
The EVAP system catches fuel vapour from the tank, stores it in a charcoal canister and later burns it in the engine. The computer tests both the flow of vapour and whether the system is sealed.
P0440 is a broad code. Many cars set a more specific one alongside it, which tells you where to look. VW, for example, lists P0440 with other EVAP codes in its purge valve bulletin.
If P0440 is the only code, work through the cheap checks first: the cap, then visible hoses, then a shop smoke test.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Loose, damaged or non-factory fuel cap
Common general cause- Why it ranks here
- EPA and makers name the cap as the easiest and most common EVAP fault to rule out.
- What would change this
- Falls if the cap is factory, clicks and the seal is good.
Cause 2: Purge valve sticking or leaking
Common general cause- Why it ranks here
- Nissan says the purge valve or its hoses usually cause purge faults, and VW lists P0440 among purge valve codes.
- What would change this
- Rises if a purge code is also stored or the valve fails a commanded vacuum test.
Cause 3: Split, cracked or disconnected EVAP hose
Common general cause- Why it ranks here
- Hose damage is a common EVAP leak source.
- What would change this
- Rises if a hose is visibly damaged or smoke escapes there.
Cause 4: Vent valve stuck or vent path blocked
Possible — needs testing- Why it ranks here
- Vent problems are a known EVAP fault, but less often the cause when no vent code is stored.
- What would change this
- Rises if P0446 or P0449 is also stored.
Cause 5: Leaking, flooded or broken-down charcoal canister
Possible — needs testing- Why it ranks here
- Topping off can saturate the canister and make it shed charcoal.
- What would change this
- Rises if the canister is heavy or leaks in a smoke test.
Cause 6: Fuel tank pressure sensor fault
Possible — needs testing- Why it ranks here
- The system relies on this sensor for its tests, and a bad reading can fail them.
- What would change this
- Rises if the reading does not move when slight vacuum or pressure is applied.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Remove and refit the fuel cap. Check it is a factory or OEM-equivalent cap, that it clicks, and that its seal is intact.
IfThe cap was loose, non-factory or its seal is damaged
It meansTighten or replace the cap and let the system re-check.
IfThe cap is good
It meansLook for other codes.
Step 2: Read all stored and pending codes with a scan tool. More specific EVAP codes point to where to look.
IfA purge code (P0441, P0443, P0496) is also stored
It meansStart at the purge valve.
IfA vent code (P0446, P0449) is also stored
It meansStart at the vent valve.
IfOnly P0440
It meansInspect the hoses.
Step 3: With the engine off and cool, look over the EVAP hoses you can reach at the purge valve, canister and filler neck.
Warning:Fuel vapour is flammable. Work outdoors with the engine off and cool, and keep sparks, cigarettes and open flames away.
IfA hose is split, cracked or off
It meansRepair the hose.
IfNothing visible
It meansA shop smoke test is next.
Step 4: Have a shop smoke test the EVAP system, then check the tank pressure sensor reading if no leak is found.
Warning:Shop test. Fuel vapour is flammable, and the setup must match the system design.
IfSmoke escapes at the canister
It meansReplace the canister.
Points to: Leaking, flooded or broken-down charcoal canister
IfNo leak, and the tank pressure reading does not respond to slight vacuum or pressure
It meansThe sensor is suspect.
Symptoms
- Check engine light on, usually with no change in how the car drives
- "Check fuel cap" message on cars that have one
- Fails an emissions or smog test because of the light or an incomplete EVAP monitor
- Persistent raw fuel smell around the car Gets more serious: stop and have it checked.
- Liquid fuel dripping under the car Gets more serious: stop and have it checked.
Compare with: Check engine light came on after getting gas
How to fix
Step 1: Check the fuel cap is a factory or OEM-equivalent part, then tighten it until it clicks.
Warning:Engine off, no smoking or flames near the filler.
Step 2: Look at the cap seal for cuts, cracks or a rolled o-ring and replace the cap if it is damaged.
Step 3: Stop filling once the pump clicks off the first time. Topping off can flood the canister.
Step 4: After a repair, drive normally for several days so the monitor can re-run. Clearing codes or disconnecting the battery resets readiness, so do it shortly before an inspection only if you then complete a drive cycle.
Parts and cost context
- Fuel (gas) cap:The cheapest first step. Replace other parts only after testing.
- EVAP canister purge valve:Usually in the engine bay, on a hose between the canister line and the intake. Labour varies, so get a quote.
- EVAP charcoal canister:If charcoal has reached the purge valve, the canister may need replacing too, or the new valve can fail again.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
VolkswagenYour car
2009–2017
Supported by vehicle dataVW bulletin 20 17 02 lists P0440 among the codes where the N80 purge valve may be involved on 2009–2017 gasoline models (except Routan). It says to smoke test and check vacuum before replacing the valve. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.
Where it is:N80 purge valve, engine bay
20 17 02Status unverified
EVAP purge valve (N80) diagnosis
2009–2017 · issued · NHTSA MC-10125657
For 2009–2017 gasoline Volkswagens (except Routan), lists the EVAP codes that can involve the N80 purge valve and says to smoke test the system and check vacuum before replacing the valve.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
P0440 questions
Can a loose gas cap really cause this code?
Yes. OBD systems can detect the vapour leak from a cap that is not tightened. After you tighten or replace it, the light should go out by itself once the system re-checks and passes on later drives, which can take several trips.
Why is P0440 so vague?
It is a general EVAP fault code. Many cars also store a more specific code, such as a purge or leak code, which tells you where to start.
Is it safe to keep driving?
Usually yes, as long as there is no strong fuel smell and no fuel dripping. Most makers advise getting it fixed when it is convenient. A strong fuel smell means get it checked soon, and dripping fuel means stop and do not drive.
Will this code fail an emissions inspection?
In states that test OBD-II, a check engine light that stays on with the engine running fails the test. Clearing the code does not help straight away, because the EVAP monitor then reads not ready until the car completes a drive cycle.
Sources and review
- Frequently Asked Questions on On-Board Diagnostics (EPA 420-F-97-003)
- On-Board Diagnostic II (OBD II) Systems Fact Sheet
- EVAP: The Phantom Emissions Menace (Nissan TechNews, May 2018)
- OBD Test Reference (rev 8.6)
- What do you mean my car is not ready?
- Recall acknowledgement 17V-088: BMW i3 REx fuel tank vent line may chafe
- Part 573 Safety Recall Report 15V-621 (Mazda 8615J): liquid fuel can enter the EVAP canister
- What To Do With the Check Engine Light (EPA420-F-00-041)
- VW 20 17 02: EVAP purge valve (N80) diagnosis
- Toyota Camry Owner's Manual (OM06291U, 2.5L A25A-FKS / 3.5L 2GR-FKS)
- Cal. Code Regs. Tit. 13, § 1968.2 — Malfunction and Diagnostic System Requirements (OBD II)
- Driveability Corner, August 2014 (Mark Warren)
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error