What does P0440 mean?
Evaporative Emission Control System Malfunction
Direct Answer
P0440 is a general EVAP system code indicating a malfunction without specifying a particular leak size. It is less common on modern OBD-II vehicles than P0442 or P0455 because newer systems are better at specifying the leak size. P0440 often means the EVAP system monitor cannot complete its self-test.
Common Symptoms
- ✓Check engine light on
- ✓Possible fuel smell
- ✓Failed emissions test
Common Causes
- 01Loose or faulty gas cap
- 02Faulty EVAP purge solenoid
- 03Failed EVAP vent solenoid
- 04Cracked charcoal canister
- 05Damaged EVAP hoses
How to Fix P0440
Replace the gas cap
Start with the cheapest fix. A new OEM-spec cap resolves P0440 in many cases.
Test the purge and vent solenoids
Both solenoids can be tested with a multimeter and by applying 12V to verify mechanical operation.
Smoke test
For leaks that are not the cap, a smoke test finds the source quickly.
Frequently Asked Questions
What is the difference between P0440 and P0442?
P0440 is a general EVAP malfunction. P0442 specifically identifies a small (0.020–0.040 inch) leak. P0440 is more common on older OBD-II systems; P0442/P0455/P0456 are the precise leak-size codes on newer systems.
Estimated Repair Cost
$15–$700
Gas cap: $15–$30. Solenoids: $50–$200 each. Full canister assembly: $200–$700.
Safe to Drive?
Yes — with caution
Completely safe to drive. Fix for emissions compliance.
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