What it means
A general fault in the evaporative emission (EVAP) system has been detected. The system seals the fuel tank and captures fuel vapour in a charcoal canister; this code indicates a failed leak test or sensor without identifying the specific failure.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The EVAP system captures fuel vapour from the tank in a charcoal canister and controls when that vapour is sent to the engine. P0440 indicates a general EVAP system malfunction, such as a failed leak check or sensor test, without identifying which component or leak is responsible.
Common causes
Most likely first.
- Fuel filler cap loose or worn
- Purge valve stuck open or closed
- Cracked EVAP hose
Symptoms
- Check engine light on
- Possible smell of fuel near tank or engine bay
- Failed emissions inspection
- Loose-cap warning may appear
How to diagnose it
- Confirm P0440 and check for accompanying EVAP codes and freeze-frame data, which may narrow down the failed test.
- Check that the fuel cap is seated correctly and inspect its seal and the filler neck for visible damage.
- Visually inspect accessible EVAP hoses, the canister, and their connections for cracks, disconnections, or damage.
- Use a scan tool to command the purge valve and check whether its operation and EVAP sensor readings respond as expected.
- If a leak remains suspected, use the manufacturer's EVAP test procedure, such as a suitable smoke test, to locate it.
Common fixes
- Refit or replace a loose or damaged fuel cap.
- Reconnect or replace a cracked EVAP hose.
- Replace a purge valve that fails its commanded-operation test.
- Repair a confirmed leak or faulty sensor in the EVAP system.
Can I keep driving?
P0440 usually does not affect normal driving, but it can cause an emissions inspection failure. If you smell fuel, make sure the cap is secure and avoid ignition sources nearby; get a strong or persistent smell checked promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.