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Home / DTC / P0440 — Missing fuel cap, Defective or damaged fuel cap, Distorted or damaged Fuel Tank Filler Neck, Torn or punctured Evaporative system hose(s), Defective Fuel Tank Sending Unit gasket or seal, Split or damaged Carbon Canister, Defective Evaporative Vent Valve and or Evaporative Purge Valve, Defective or damaged fuel tank

P0440 — Missing fuel cap, Defective or damaged fuel cap, Distorted or damaged Fuel Tank Filler Neck, Torn or punctured Evaporative system hose(s), Defective Fuel Tank Sending Unit gasket or seal, Split or damaged Carbon Canister, Defective Evaporative Vent Valve and or Evaporative Purge Valve, Defective or damaged fuel tank

Detailed page for trouble code P0440.

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P0440

AUDI P — Powertrain

Missing fuel cap, Defective or damaged fuel cap, Distorted or damaged Fuel Tank Filler Neck, Torn or punctured Evaporative system hose(s), Defective Fuel Tank Sending Unit gasket or seal, Split or damaged Carbon Canister, Defective Evaporative Vent Valve and or Evaporative Purge Valve, Defective or damaged fuel tank

Brand: AUDI
Type: P — Powertrain
Views: UK: 30 EN: 68 RU: 66
AI status
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Page language: EN

Causes

  • Loose, missing or defective fuel cap
  • Distorted or damaged fuel tank filler neck or cap seal
  • Torn, cracked or disconnected EVAP hoses or fittings
  • Split or saturated charcoal canister
  • Defective evaporative vent (canister purge) valve or purge solenoid
  • Defective vent valve (vent control) or stuck open/closed

Symptoms

  • Check Engine Light (MIL) illuminated
  • Possible faint fuel/vapor smell near fuel tank or filler neck
  • Failed emissions test or readiness monitor for EVAP
  • No other driveability symptoms in many cases

What to check

  • Read stored DTC(s) and freeze frame data with a scan tool; record pending/history
  • Visually inspect fuel cap for damage and verify it threads/seals correctly
  • Verify fuel cap is tightened properly (clicks) and retest
  • Perform a visual inspection of EVAP hoses, lines, and connectors for cracks, disconnections or abrasions
  • Inspect charcoal canister for cracks, saturation or physical damage
  • Inspect fuel filler neck and fuel tank filler seal for distortion or damage

Signal parameters

  • Fuel tank pressure sensor: near atmospheric (0 kPa gauge) at rest; changes when commanded leak test
  • Purge valve: commanded open/closed by PCM; should show corresponding flow or pressure change
  • Vent valve: commanded states (open to atmosphere or closed to allow pressure change) and should respond when commanded
  • No large uncontrolled pressure drops/leaks observed during a smoke or pressure test
  • Scan tool EVAP monitor status: ready/complete or failed/pending
  • Purge flow vs. commanded duty cycle — purge should flow when commanded and be closed when not commanded

Diagnostic algorithm

  1. Connect a scan tool, read and record DTCs and freeze frame. Note other EVAP-related codes (P0441, P0442, etc.).
  2. Verify simple causes: check fuel cap is present, properly tightened and undamaged; replace cap if doubtful and clear codes.
  3. Visually inspect filler neck, cap seal, hoses, charcoal canister, and tank area for damage, disconnection or contamination.
  4. If visual inspection is inconclusive, perform a smoke test to locate external leaks (filler neck, hoses, seams, canister).
  5. Command EVAP purge valve and vent valve via scan tool; verify they actuate and check for expected pressure/flow changes. Replace if nonfunctional.
  6. Test fuel tank pressure sensor and related wiring; compare live readings to expected values during a pressure/smoke test.
  7. If leak is not found externally, isolate sections (cap/filler, purge valve, canister) and retest to narrow source.
  8. Inspect and test seals at fuel tank sending unit and filler neck; replace gaskets/seals if leaking.
  9. If charcoal canister is physically damaged or saturated, replace and retest.
  10. Repair or replace confirmed faulty components, clear codes, then perform drive cycle and EVAP monitor checks to ensure the system completes and the DTC does not return.

Likely causes

  • Loose, missing or improperly seated fuel cap
  • Damaged or degraded fuel cap seal or filler neck
  • Leaking/cracked EVAP hose or connection
  • Faulty purge valve (stuck or not responding)
  • Faulty vent/vent control valve
  • Leaking or saturated charcoal canister

Fault status

⚠️ Status
P0440 — Evaporative Emission Control System Malfunction. MIL illuminated. Possible EVAP leakage or component failure; further diagnosis required.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

P0441 P0442 P0455 P0456 P0457 P0446
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