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P0440 — EVAP System Malfunction (Generic)

P0440 is a generic evaporative emission (EVAP) system fault. The EVAP system captures fuel vapors from the tank and routes them through the charcoal canister to be burned by the engine instead of vented into the atmosphere. P0440 is set when the ECM detects that this sealed system has lost its ability to hold pressure or vacuum during a leak test. It is almost always the first sign of a small leak somewhere between the fuel tank and the engine intake.

P0440 means evap system malfunction (generic). A vehicle usually stays drivable short-term with this code, but it should be diagnosed promptly. The most common cause is loose, worn, or wrong-spec fuel cap (typically $15–$60). Causes and cost vary by make and model; confirm the root cause before replacing parts.

Severity: low powertrain Safe to drive (short term)

Reviewed by MECH AI Editorial · Last verified

What does P0440 mean?

P0440 is a generic evaporative emission (EVAP) system fault. The EVAP system captures fuel vapors from the tank and routes them through the charcoal canister to be burned by the engine instead of vented into the atmosphere. P0440 is set when the ECM detects that this sealed system has lost its ability to hold pressure or vacuum during a leak test. It is almost always the first sign of a small leak somewhere between the fuel tank and the engine intake.

What are the symptoms of P0440?

What causes P0440?

Cause Likelihood Estimated repair (USD)
Loose, worn, or wrong-spec fuel cap — Always the first thing to check — costs nothing to tighten or replace. Most common $15–$60
Cracked, kinked, or disconnected EVAP hose Common $30–$200
Failed EVAP purge valve (purge solenoid) stuck open or closed Common $80–$300
Failed EVAP canister vent valve / vent solenoid Common $80–$350
Cracked or damaged EVAP charcoal canister Occasional $200–$600
Pinhole leak in fuel filler neck or tank seam Occasional $150–$800
Failed fuel tank pressure sensor Occasional $100–$350

Repair costs are typical US ranges and vary by make, model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.

Is it safe to drive with P0440?

In most cases a vehicle stays drivable for short trips with P0440 active, but you should diagnose and repair it promptly. This is a low-severity code — ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on your specific make and model.

How to diagnose P0440

  1. Inspect and re-seat the fuel cap

    Remove the fuel cap and check the rubber gasket for damage, debris, or twisting. Reinstall hand-tight until the cap clicks. Many vehicles require 3+ click stops. Clear the code and drive several drive cycles to allow the EVAP monitor to retest.

    Tools: None

  2. Read mode 6 / EVAP monitor data

    Pull mode 6 test results for the EVAP system. Look at the small-leak, large-leak, and purge flow test IDs. The specific test that failed narrows the diagnosis from "EVAP system" to which subsystem within it.

    Tools: Scan tool with mode 6 support

  3. Smoke-test the EVAP system

    Introduce low-pressure smoke (typically 0.5 psi) into the EVAP service port. Inspect every hose joint, the charcoal canister, the purge and vent solenoids, the filler neck, and the tank top. Smoke escaping anywhere is the leak — repair it and retest.

    Tools: EVAP smoke machine, UV dye and light (optional), Inspection mirror

  4. Bench-test the purge valve and vent valve

    Remove the purge valve and apply 12 V across its terminals. It should click and open. With no voltage, it should hold vacuum. The vent valve operates in reverse — normally open, closes when energized. Either valve stuck the wrong way will set P0440.

    Tools: 12 V test source, Hand vacuum pump

  5. Check the fuel tank pressure sensor reading

    Compare the live tank pressure PID to a known-good vehicle. A reading that does not change when the cap is removed or when the purge valve is commanded indicates either a failed sensor or a blocked hose to it.

    Tools: Scan tool

How do I fix P0440?

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P0440: frequently asked questions

What does diagnostic trouble code P0440 mean?

P0440 is a generic evaporative emission (EVAP) system fault. The EVAP system captures fuel vapors from the tank and routes them through the charcoal canister to be burned by the engine instead of vented into the atmosphere. P0440 is set when the ECM detects that this sealed system has lost its ability to hold pressure or vacuum during a leak test. It is almost always the first sign of a small leak somewhere between the fuel tank and the engine intake.

What are the symptoms of P0440?

Check Engine Light is illuminated. Faint fuel smell when filling the tank or shortly after. No drivability problem in most cases. Fuel-cap warning light on some vehicles. Vehicle will fail emissions / smog testing

What causes P0440?

Loose, worn, or wrong-spec fuel cap (most-common). Cracked, kinked, or disconnected EVAP hose (common). Failed EVAP purge valve (purge solenoid) stuck open or closed (common). Failed EVAP canister vent valve / vent solenoid (common). Cracked or damaged EVAP charcoal canister (occasional). Pinhole leak in fuel filler neck or tank seam (occasional). Failed fuel tank pressure sensor (occasional)

Is it safe to drive with P0440?

In most cases a vehicle stays drivable for short trips with P0440 active, but it should be diagnosed and repaired promptly — this is a low-severity code. Ignoring it can lead to further damage or a failed emissions test. Specific tolerance varies by make and model.