Gas cap missing, loose, damaged or not sealing (both sources). Failed purge valve (solenoid) or vent valve. Plugged, split or damaged charcoal (carbon) canister. Cut, torn or disconnected EVAP hoses. Damaged fuel tank filler neck, a leaking fuel tank sending-unit seal, or a damaged fuel tank (listed by RepairPal). A fuel tank pressure sensor that misreads, so the PCM thinks no vacuum is being created (RepairPal).

Reseat or replace the gas cap. Repair cut, torn or disconnected EVAP hoses. Replace a faulty purge valve, vent valve, charcoal canister or fuel tank pressure sensor found by testing.

P0440🌫 Emissions / EVAPUsually OK to drive

P0440: Evaporative Emission (EVAP) Control System Malfunction (Meaning, Causes, Fixes)

Q: What does P0440 mean?

P0440 means the PCM found a problem in the EVAP system, which captures fuel vapor so it doesn't escape. Start with the gas cap, then check hoses and the purge and vent valves. The EVAP system routes fuel vapor from the tank to a charcoal canister for storage. Later, with the engine running, a purge valve opens and intake vacuum draws those vapors into the engine to be burned. P0440 is a generic code meaning part of that system is no longer working correctly. The sources word it differently: OBD-Codes.com defines it broadly as an EVAP control system malfunction, while RepairPal defines it as "Evaporative System Malfunction, Large Leak." RepairPal adds that "large leak" is somewhat misleading: what the code really means is that the system couldn't build or hold vacuum during its leak test, as measured by the fuel tank pressure sensor. RepairPal says the PCM sets P0440 when the vacuum decays much faster than specified, or when no vacuum is reached on two consecutive tests.

Q: Can I keep driving with P0440?

Usually OK to drive. Usually safe to keep driving: OBD-Codes.com says you likely won't notice drivability problems. RepairPal rates it moderate, so get it diagnosed within a reasonable time, and sooner if you smell fuel.

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0440 means

The EVAP system routes fuel vapor from the tank to a charcoal canister for storage. Later, with the engine running, a purge valve opens and intake vacuum draws those vapors into the engine to be burned. P0440 is a generic code meaning part of that system is no longer working correctly. The sources word it differently: OBD-Codes.com defines it broadly as an EVAP control system malfunction, while RepairPal defines it as "Evaporative System Malfunction, Large Leak." RepairPal adds that "large leak" is somewhat misleading: what the code really means is that the system couldn't build or hold vacuum during its leak test, as measured by the fuel tank pressure sensor. RepairPal says the PCM sets P0440 when the vacuum decays much faster than specified, or when no vacuum is reached on two consecutive tests.

Severity: can I keep driving?

Usually OK to drive

Usually safe to keep driving: OBD-Codes.com says you likely won't notice drivability problems. RepairPal rates it moderate, so get it diagnosed within a reasonable time, and sooner if you smell fuel.

Common symptoms

Check engine light on
Usually no drivability problems (both sources)
Sometimes a fuel smell from escaping fuel vapor (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Gas cap missing, loose, damaged or not sealing (both sources)
Failed purge valve (solenoid) or vent valve
Plugged, split or damaged charcoal (carbon) canister
Cut, torn or disconnected EVAP hoses
Damaged fuel tank filler neck, a leaking fuel tank sending-unit seal, or a damaged fuel tank (listed by RepairPal)
A fuel tank pressure sensor that misreads, so the PCM thinks no vacuum is being created (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Remove and reinstall the gas cap, clear the code, and drive for a day to see if it comes back (OBD-Codes.com).
Check that the cap's seal isn't dry or cracked. If it is, replace the cap.
Look over the EVAP hoses you can reach, especially around the purge solenoid, for cuts, holes or disconnected lines.

Typical fixes

Reseat or replace the gas cap
Repair cut, torn or disconnected EVAP hoses
Replace a faulty purge valve, vent valve, charcoal canister or fuel tank pressure sensor found by testing

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

A smoke test of the whole EVAP system, which both sources recommend for finding leaks you can't see.
Watching fuel tank pressure readings on a scan tool to confirm the fuel tank pressure sensor works, since the PCM relies on it for the leak test (RepairPal).
Checking that the purge and vent valves hold vacuum for at least 30 to 60 seconds (RepairPal).
Inspecting the filler neck, canister and fuel tank, including the seal where the fuel pump and sending unit mount. RepairPal notes this seal sometimes isn't replaced or seated properly after a fuel pump job.

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Will P0440 go away on its own?

RepairPal says most codes disappear once the onboard system no longer detects the issue. If you've fixed a loose gas cap, it can take a few drives for the EVAP test to run again and the light to clear. If the code stays, get it diagnosed.

Is P0440 the same as P0455?

They're closely related. RepairPal describes both as large-leak or no-vacuum EVAP faults, and they share the same common causes, starting with the gas cap. OBD-Codes.com treats P0440 as a broader EVAP system malfunction code.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.