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Home › Lexus › 1998 › SC 300 › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes › Diagnostic Tests › DTC P0440: EVAP System Malfunction › Diagnosis & Repair

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 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'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 filler cap and gasket. Replace fuel cap as necessary. If fuel filler cap and gasket are okay, go to next step.
  5. Remove fuel filler cap. Visually inspect fuel 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 vapor pressure sensor VSV, and between vapor pressure sensor 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 behind glove box. Turn ignition on. Backprobing, measure voltage between terminals No. 2 (Blue/Black wire) and No. 18 (Brown wire) at ECM E16 harness 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.
  10. Backprobing ECM harness connector, measure voltage between terminals No. 18 (Red wire) at ECM E18 harness connector and No. 18 (Brown wire) at ECM E16 harness connector. Disconnect vacuum hose from vapor pressure sensor. Sensor is located next to charcoal canister. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied, and .5 volt or less with 1.2-19.7 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 in wiring harness between vapor pressure sensor and ECM. See appropriate wiring diagram in SYSTEM WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace vapor pressure sensor.
  12. Disconnect fuel tank-to-charcoal canister vacuum hose from charcoal canister. Ensure fuel filler 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 P0440 to set was an incorrectly installed fuel tank cap.
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