P0440

Code

Generic P — Powertrain

EVAP System

Brand: Generic

Type: P — Powertrain

Views: UK: 42 EN: 76 RU: 83

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Loose, damaged, or missing fuel filler cap
Evaporative system leak (hoses, fittings, fuel tank)
Faulty purge valve (solenoid) or stuck open/closed
Faulty vent/canister purge shut valve (vent solenoid)
Saturated or damaged charcoal canister
Faulty fuel tank pressure or EVAP pressure sensor

Symptoms

Malfunction Indicator Lamp (MIL/CEL) illuminated
Failed emissions or smog test
Occasional fuel smell near vehicle
Poor evaporative system performance (may not affect driveability)
Difficulty starting after refueling (less common)

What to check

Scan for stored and pending trouble codes and freeze-frame data
Visually inspect fuel cap for damage and proper fit; check cap torque/locking
Perform visual inspection of EVAP hoses, fittings, and charcoal canister
Check wiring and connectors to purge and vent solenoids and sensors
Monitor live data: purge valve command, vent valve state, tank pressure sensor
Perform smoke test/pressure test to locate leaks

Signal parameters

Purge valve command (PCM): on/off or duty-cycle percentage when commanded to purge
Purge valve coil resistance: compare to OEM specification
Vent/vent control valve state: open at key-on/closed when commanded (verify operation)
Fuel tank/tank pressure sensor: near ambient when sealed; shows negative pressure or change when purged
Reported leak detection pump or monitor values (if equipped): used by PCM to infer leaks
OBD monitor status: EVAP readiness/incomplete tests after clearing codes

Diagnostic algorithm

Retrieve all EVAP-related codes and freeze-frame data. Note drive cycle status and readiness monitors.
Inspect fuel filler cap for damage, proper sealing, and locking. Replace or tighten cap if suspect, then clear codes and test drive.
Visually inspect EVAP hoses, quick-connects, and canister for cracks, disconnections, or damage.
Monitor live data while commanding the purge valve ON/OFF (via scan tool). Confirm the valve responds and that intake manifold vacuum is applied to the EVAP system when commanded.
Command vent/vent control valve and verify open/closed states; check for continuity and proper resistance of solenoids.
Perform a smoke test or pressure/leak test on the EVAP system to locate leaks at fittings, hoses, tank seams, or the canister.
If no external leaks found, inspect and test the fuel tank pressure sensor and its wiring. Replace if out of spec.
If purge or vent solenoids fail the bench or active tests, replace the faulty unit and retest.
If charcoal canister is saturated, damaged, or crushed, replace and retest system.
After repairs, clear codes and run drive cycle or readiness tests to verify the EVAP monitor completes and code does not return.

Likely causes

Loose or defective fuel cap
Leaking hose or fitting in EVAP plumbing
Defective purge valve
Faulty vent/vent control valve
Canister damage or blockage

Fault status

⚠️ Status

Evaporative Emission Control System Malfunction detected by PCM. MIL illuminated. Could be due to leaks, faulty valves, sensors, or wiring. Vehicle may fail emissions testing until repaired.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-4 hours