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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 Lexus Scan Tool)

Diagnosis & Repair (Using Lexus 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 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 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. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Using scan tool, select ACTIVE TEST mode. Disconnect vacuum hose from charcoal canister at EVAP VSV. See Fig 1. Start engine. Connect a vacuum gauge to disconnected vacuum hose. Using scan tool, activate EVAP VSV. When EVAP VSV is activated, vacuum should be present. When EVAP VSV is not activated, no vacuum should be present. If vacuum is as specified, go to step  18. If vacuum is not as specified, go to next step.
  15. Turn ignition off. Check for correct routing, looseness, damage and blockage in vacuum hoses between intake manifold and EVAP VSV, and between EVAP VSV and charcoal canister. Repair as necessary. If hoses are okay, go to next step.
  16. Check EVAP VSV. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If EVAP VSV is not okay, replace EVAP VSV and charcoal canister. Also clean vacuum hoses between throttle body and EVAP VSV, and EVAP VSV and charcoal canister. If EVAP VSV is okay, go to next step.
  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. Turn ignition off. Disconnect canister closed valve VSV vacuum hose. VSV has a Gray 2-pin connector and is located near mass airflow meter. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Select ACTIVE TEST mode on scan tool. Using scan tool, turn canister closed valve VSV on. Apply compressed air to port "A" of canister closed valve VSV. Air should not flow from port "B". See Fig 2. Using scan tool, turn canister closed valve VSV off. Air should flow from port "B". If VSV operates correctly, go to step  21. If VSV does not operate correctly, go to next step.
  19. Check canister closed valve VSV. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If canister closed valve VSV is not okay, replace canister closed valve VSV and charcoal canister. Also clean vacuum hoses between charcoal canister and canister closed valve VSV. If canister closed valve VSV is okay, check vacuum hose between canister closed valve VSV and charcoal canister for looseness, damage and blockage. Replace vacuum hose as necessary. If vacuum hose is okay, go to next step.
  20. 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.
  21. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Ensure ignition is on. Select ACTIVE TEST mode on scan tool. 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 vacuum hoses from pressure switching valve VSV. Using scan tool, activate pressure switching valve VSV. Apply compressed air to port "E" of pressure switching valve VSV. Air should flow from port "F". See Fig 3. Using scan tool, turn pressure switching valve VSV off. Air should not flow from port "F". If VSV operates correctly, go to step  24. If VSV does not operate correctly, go to next step.
  22. 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.
  23. 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.
  24. Access ECM under front of carpet on passenger side of vehicle. Backprobing ECM harness connector, connect DVOM between terminal No. 22 (Red wire) at ECM E18 connector and terminal No. 18 (Brown wire) at ECM E16 connector. See Fig 4. Select ACTIVE TEST mode on scan tool. Start engine. EVAP VSV, canister closed valve VSV and pressure switching valve VSV should all be on. Observing DVOM, when voltage reaches 1.2 volts, switch EVAP VSV and pressure switching valve VSV off. See Fig 4. Wait 30 seconds and note DVOM voltage reading. If voltage stays at 1.2 volts, fuel tank is okay. Go to next step. If voltage does not stay at 1.2 volts, replace fuel tank.
  25. Access ECM under front of carpet on passenger side of vehicle. Backprobing ECM harness connector, connect DVOM between terminal No. 22 (Red wire) at ECM E18 connector and terminal No. 18 (Brown wire) at ECM E16 connector. See Fig 5. Select ACTIVE TEST mode on scan tool. Start engine. EVAP VSV, canister closed valve VSV and pressure switching valve VSV should all be on. Observing DVOM, when voltage reaches 1.2 volts, switch EVAP VSV off. See Fig 5. Wait 30 seconds and note DVOM voltage reading. If voltage stays at 1.2 volts, go to next step. If voltage does not stay at 1.2 volts, replace charcoal canister.
  26. 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.
Fig 1: Testing EVAP VSV
G99I52843Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 2: Identifying Canister Closed Valve VSV Vacuum Ports
G99D52749Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 3: Identifying Pressure Switching Valve VSV Vacuum Ports
G99A52753Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 4: Checking Fuel Tank By Measuring PTNK Circuit Voltage At ECM
G99C52755Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 5: Checking Charcoal Canister By Measuring PTNK Circuit Voltage At ECM
G99E52757Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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