P0440 - Evaporative Emission (EVAP) System Malfunction
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0440 is a generic OBD-II code indicating a malfunction in the Evaporative Emission (EVAP) system. The EVAP system's job is to trap fuel vapors before they escape into the atmosphere. The ECU monitors the system's integrity by performing a leak test (vacuum or pressure decay). P0440 is triggered when the system detects that it cannot maintain the required vacuum or pressure levels, indicating a leak or a failure in a control component. Unlike P0442 or P0455, which specify leak sizes, P0440 is often used as a general system failure code.
Possible Causes
Loose, damaged, or incorrect gas cap
Leaking or cracked EVAP system hoses or lines
Faulty Purge Valve or Vent Valve
Cracked or damaged charcoal canister
Faulty Fuel Tank Pressure (FTP) sensor
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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