What P0440 means
P means powertrain (engine and transmission). The 0 marks a generic code defined by SAE, so the same number means the same thing across makes. The third character, 4, places it in the auxiliary emission controls subsystem; the last two digits identify the specific fault.
The EVAP system traps fuel vapour from the tank in a charcoal canister and later burns it in the engine. The engine computer periodically seals the system and checks whether it holds pressure or vacuum; a leak test failure sets a code sized by how large the leak appears to be.
What “System” means here
A system-level fault for the evaporative emission (EVAP) system: the module's overall test of the system failed rather than a specific circuit. Check for other codes that narrow it down, then work through the system's components.
What you may notice
Symptoms depend on the vehicle and on how the module responds to the fault. Any of these can accompany P0440:
- Usually no drivability symptom
- Fuel smell near the vehicle
- Failed inspection
Where to start diagnosing P0440
- Check the fuel cap first: seal condition, correct cap, and that it clicks fully closed.
- Inspect EVAP hoses around the canister and filler neck for cracks.
- A smoke test is the most reliable way to find small EVAP leaks.
- Check the purge and vent valves seal when closed.
Clear the code only after recording freeze frame data: it shows the engine speed, load and temperature at the moment the fault set, which is often the best clue to reproducing it.
Live data to watch
These standard OBD2 values relate to P0440. Support varies by vehicle; a value your car does not report will simply be missing.
| Value | What to look for |
|---|---|
| EVAP system vapour pressure (PID 0x32) | Watch it during the leak test where the tool allows. |
| Commanded evaporative purge (PID 0x2E) | Purge activity. |
| Fuel tank level (PID 0x2F) | Many leak tests only run within a fuel level window. |
Related codes
Codes from the same evaporative emission (EVAP) system family. If several are stored together, the shared part — wiring, a common reference voltage, or the component itself — is the place to start.
Further reading
Frequently Asked Questions
What does P0440 mean?
P0440 is the generic SAE J2012 code for "Evaporative Emission System". In plain terms, it means the engine computer's evaporative emission (EVAP) system monitor has reported "Evaporative Emission System".
Can I keep driving with P0440?
Drivable. The fault affects fuel vapour control and inspection readiness, not engine operation.
What should I check first for P0440?
Check the fuel cap first: seal condition, correct cap, and that it clicks fully closed.
Definition source: SAE J2012 / ISO 15031-6 generic DTC definitions. This is the generic meaning that applies across makes; a manufacturer can define a code more narrowly or add its own sub-codes, so confirm against the service information for your vehicle before replacing parts. Written by the OBDAssistant engineering team — see our editorial policy.