What P0440 means
The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air.
How the engine computer detects it
P0440 is the general code for a fault in this system without further narrowing down – leak, purge flow or component. Today most makers use the specific codes instead (P0441 ff, P0455–P0457, P0496); the GM and Ford tables of 2006–2023 do not contain P0440. It appears in VW code lists and in an FCA bulletin for the Alfa Romeo 2.0, fixed by software, where FCA calls it incorrect flow. What sets it is therefore manufacturer-specific; CARB requires purge flow and leaks to be monitored.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Possibly slight fuel smell
- Readiness or emission inspection not passed
- No change in driving
Common causes
- Fuel cap leaking, loose or wrong Most likely
- Purge valve leaking or sticking Possible
- Leaking or cracked EVAP hoses, canister or vent valve Possible
- Engine module software Less likely
How to diagnose P0440
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: evap system, fuel cap, evap purge valve, charcoal canister.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P0440 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Dodge Durango | 2003–2018 | 4 | 24k | |
| Chevrolet Trailblazer EXT | 2003–2004 | 4 | 40k |
Counts of owner complaints to the NHTSA that mention P0440 (31 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 4
- Auxiliary emission controls
- 40
- Specific fault
Questions drivers ask
Can I drive with code P0440?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0440?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0440 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0440 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0440. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.