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Home >> Lexus >> 1996 >> LS 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0440 - EVAP System Malfunction >> Diagnosis & Repair
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Diagnosis & Repair

  1. Check with vehicle driver if fuel tank cap was loose when refueling. If fuel tank cap was loose prior to refueling, it probably was cause of DTC to set. If fuel tank cap was not loose, check for cracks, deformations or loose connections in the 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 cap. If fuel tank cap is an original manufacturer cap, go to next step. If fuel tank cap is not an original manufacturer 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 VSV for vapor pressure sensor, and between vapor pressure sensor 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 harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals No. 1 (Blue/Red wire) and No. 22 (Brown wire) at ECM E13 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.
  10. Backprobing ECM harness connector, measure voltage between terminals No. 18 (Pink/Green wire) at ECM E11 connector and No. 22 (Brown wire) at ECM E13 connector. Disconnect vacuum hose from vapor pressure sensor. Sensor is located in left front of engine compartment. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied and less than .5 volt with 1.2 in. Hg applied, go to step 12). If voltage is not as specified, go to next step.
  11. Check for an open or short in wiring harness between vapor pressure sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace vapor pressure sensor.
  12. Disconnect vacuum hose from charcoal canister. Ensure fuel tank cap is installed properly. Using compressed air, apply .71 psi (.05 kg/cm2 ) to fuel tank. If tank does not hold pressure for a minimum of one minute, replace fuel tank. If tank holds pressure, no fault is indicated at this time. Probable cause of DTC to set was an incorrectly installed fuel tank cap.
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