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Home >> Lexus >> 2000 >> SC 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0441: Incorrect EVAP Purge Flow Or DTC P0446: EVAP Vent Control Fault >> Diagnosis & Repair (Using OBD-II Scan Tool)

Diagnosis & Repair (Using OBD-II Scan Tool)

  1. 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 cap, replace cap with a manufacturer's cap.
  3. Check if fuel tank cap is installed properly. Reinstall fuel cap as necessary. If fuel cap is installed properly, go to next step.
  4. Check for damaged fuel tank cap and gasket. Replace fuel tank 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. Check EVAP VSV, canister closed valve VSV, pressure switching valve VSV and vapor pressure sensor wiring harness connectors for damaged pins, corrosion and loose wires. Repair as necessary. If connectors are okay, go to next step. For component locations, see appropriate illustration in THEORY & OPERATION article.
  9. Check all EVAP related vacuum hoses between fuel tank and charcoal canister, and between fuel tank and fuel tank overfill check valve for damage, blockage, looseness and correct routing. Repair as necessary. If vacuum hoses are okay, go to next step. For proper vacuum hose routing, see appropriate illustration in VACUUM DIAGRAMS article.
  10. Access ECM under front of carpet on passenger side of vehicle. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals No. 2 (Blue/Black wire) and No. 18 (Brown wire) at ECM E16 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: Vehicle may be equipped with one of 2 different types of vapor pressure sensor. Sensor is mounted on top of fuel tank and may either have 2 vacuum ports (old style) or no vacuum ports (new style).
  11. Locate vapor pressure sensor on top of fuel tank. Sensor has a Black 3-pin connector with Brown, Blue/Black and Red wires. Identify type of vapor pressure sensor used. If sensor does not have any vacuum ports, go to next step. If sensor has 2 vacuum ports, disconnect vacuum supply hose from vapor pressure sensor. See Figure. Backprobing ECM harness connector, connect voltmeter between terminal No. 22 (Red wire) at ECM E18 connector and terminal No. 18 (Brown wire) at ECM E16 connector. See Figure. Connect a vacuum pump to sensor. Voltage should be 3.0-3.6 volts without vacuum applied, and 1.3-2.1 volts with .59 in. Hg (2.0 kPa) applied. If voltage is as specified, go to step  14. If voltage is not as specified, go to step  13.
  12. Backprobing ECM harness connector, connect voltmeter between terminal No. 22 (Red wire) at ECM E18 connector and terminal No. 18 (Brown wire) at ECM E16 connector. See Figure. Remove fuel tank cap and note voltmeter reading. If voltage is 3.0-3.6 volts, go to step  14. If voltage is not 3.0-3.6 volts, go to next step.
  13. 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.
  14. Disconnect EVAP VSV vacuum hoses. For EVAP VSV location, see appropriate illustration in THEORY & OPERATION article or VACUUM DIAGRAMS article. Turn ignition on. Access ECM under front of carpet on passenger side of vehicle. Backprobing, connect a fused jumper wire between ground and terminal No. 7 (Green/Red wire) at ECM E16 connector. See Figure.
  15. Apply compressed air to EVAP VSV port "E". See Fig 1. Air should flow from port "F". Remove fused jumper wire. Air should not flow from port "F". If EVAP VSV functions as specified, go to step  18. If EVAP VSV does not function as specified, go to next step.
    Fig 1: Identifying EVAP VSV Vacuum Ports
    G96D09634Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  16. Check EVAP VSV operation. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If VSV is okay, go to next step. If EVAP VSV is not okay, replace EVAP VSV as necessary. Also clean vacuum hose between throttle body and EVAP VSV, and EVAP VSV and charcoal canister, then check charcoal canister. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
  17. Check for an open or short in wiring harness between EFI main relay, EVAP VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest system.
  18. Disconnect canister closed valve VSV vacuum hose. VSV has a Gray 2-pin connector and is located near mass airflow meter. Access ECM under front of carpet on passenger side of vehicle. Turn ignition on. Backprobing, connect a fused jumper wire between ground and terminal No. 12 (White wire) at ECM E20 connector. See Figure. Apply compressed air to VSV port "A". See Figure.
  19. Air should not flow from VSV port "B". Disconnect fused jumper wire. Air should flow from port "B". If VSV does not function as specified, go to next step. If VSV functions as specified, go to step  22.
  20. Check canister closed valve VSV. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If VSV is okay, go to next step. If VSV is not okay, replace canister closed VSV and charcoal canister. Also clean vacuum hose between charcoal canister and canister closed valve VSV.
  21. Check for an open or short in wiring harness between EFI main relay, canister closed valve VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest system.
  22. Turn ignition on. Access ECM under front of carpet on passenger side of vehicle. Backprobing, connect a fused jumper wire between ground and terminal No. 10 (White/Blue wire) at ECM E18 connector. See Figure. Locate pressure switching valve VSV on charcoal canister or on top of fuel tank. Pressure switching valve VSV has 2 vacuum ports and a Brown 2-pin connector with White/Blue and Black/Red wires. Disconnect pressure switching valve VSV vacuum hoses. Apply compressed air to VSV port "E". See Figure. Air should flow from port "F". Remove fused jumper wire. Air should not flow from port "F". If VSV functions as specified, go to step  25. If VSV does not function as specified, go to next step.
  23. Check pressure switching valve VSV. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If pressure switching valve VSV is not okay, replace pressure switching valve VSV and charcoal canister. Also clean vacuum hose between charcoal canister and pressure switching valve VSV, and between pressure switching valve VSV and fuel tank. If pressure switching valve VSV is okay, go to next step.
  24. Check for an open or short in wiring harness between EFI main relay, pressure switching valve VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest system.
  25. Charcoal canister or fuel tank overfill check valve maybe defective. Check fuel evaporation system. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. If no problem is indicated, replace ECM.
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