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Home >> Lexus >> 2002 >> SC 430 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0440: EVAP System Malfunction >> Diagnosis & Repair
July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

Diagnosis & Repair

  1. Check with vehicle driver if fuel tank cap was found loose at any time. If fuel tank cap was loose, it probably was cause of DTC P0440 setting. If fuel tank cap was not loose, check for cracks, deformations or loose connections in following:
    • Fuel tank.
    • Charcoal canister.
    • Fuel tank filler pipe.
    • Hose and tubes around fuel tank and charcoal canister.

    Repair as necessary. If components are okay, go to next step.

  2. Check if fuel tank cap is an original manufacturer's cap. If fuel tank cap is an original manufacturer's cap, go to next step. If fuel tank cap is not an original manufacturer's cap, replace cap with a manufacturer's cap.
  3. Check if fuel cap is installed properly. Reinstall cap as necessary. If fuel cap is installed properly, go to next step.
  4. Check for damaged fuel tank cap and gasket. Replace fuel cap as necessary. If fuel tank cap and gasket are okay, go to next step.
  5. Remove fuel tank cap. Visually inspect fuel tank filler neck for damage. Replace filler neck as necessary. If filler neck is okay, go to next step.
  6. Check vacuum hoses between vapor pressure sensor and fuel tank, and between pressure switching valve VSV and charcoal canister. Check hoses for correct installation, looseness and damage. Repair as necessary. If vacuum hoses are okay, go to next step.
  7. Check hose and tube between fuel tank and charcoal canister for correct installation and damage. Repair as necessary. If hose and tube are okay, go to next step.
  8. Visually inspect charcoal canister for cracks or damage. Replace canister as necessary. If canister is okay, go to next step.
  9. Access ECM at left front of engine compartment. Turn ignition on. Backprobing connector, measure voltage between terminals No. 27 (Green/White wire) and No. 26 (Green wire) at ECM E5 connector. See Figure. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest system.
    NOTE: DO NOT apply more than 19.7 in. Hg of vacuum to vapor pressure sensor.
  10. Backprobing ECM harness connector, measure voltage between terminals No. 25 (Brown/White wire) and No. 26 (Green wire) at ECM E5 connector. Disconnect vacuum supply hose (hose closest to electrical connector) from vapor pressure sensor. Sensor is mounted on charcoal canister and is located next to fuel tank. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied, and .5 volt or less with 1.2 in. Hg of vacuum applied, go to step  12. If voltage is not as specified, go to next step.
  11. Check for an open or short circuit in wiring harness between vapor pressure sensor and ECM. See WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace vapor pressure sensor.
  12. Fuel tank or fuel tank overfill check valve may be defective. Check fuel evaporation system. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - GS300, IS300, GS430, LS430 & SC430 article. Repair as necessary. If no problem is indicated, probable cause of DTC P0440 to set was an incorrectly installed fuel tank cap.
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