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Diagnosis & Repair (Using Lexus Scan Tool)

WARNING: This page is about a different car, the 2002 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check for cracks, deformations or loose connections in hoses and tubes around fuel tank and charcoal canister. See Figure. 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 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. See Figure. 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 for loose or disconnected connectors at EVAP VSV, canister closed valve VSV, pressure switching valve VSV and vapor pressure sensor. Repair as necessary. If all connectors are okay, go to next step.
  9. Check for correct routing, damage, looseness and blockage in following vacuum hoses:
    • Between EVAP VSV and charcoal canister.
    • Between overfill check valve and charcoal canister.
    • Between fuel filler pipe and overfill check valve.
    • Between fuel filler pipe and top of fuel tank.

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

  10. Access ECM at left front of engine compartment. Turn ignition on. Backprobing, measure voltage between terminals No. 35 (Blue/Yellow wire) and No. 34 (Brown 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.
  11. Backprobing ECM harness connector, measure voltage between terminals No. 25 (Blue/Yellow wire) at ECM E5 connector and No. 34 (Brown wire) at ECM E5 connector. See Figure. Disconnect vacuum supply hose from vapor pressure sensor. Connect a vacuum/pressure pump to sensor vacuum port. 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. Apply .22 psi of pressure to vacuum port. Voltage should be 4.2-4.8 volts. If voltage is as specified, go to step  13. If voltage is not as specified, go to next step.
  12. Check for an open or short in wiring harness between vapor pressure sensor and ECM. See WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace vapor pressure sensor.
  13. Connect Lexus scan tool to Data Link Connector (DLC) No. 3. See Figure. Using scan tool, select ACTIVE TEST mode. Disconnect EVAP VSV vacuum hose from charcoal canister. See Fig 1. Start and run engine. Check for vacuum at vacuum hose when EVAP VSV is activated by scan tool. Vacuum should exist with EVAP VSV switched on. Vacuum should not exist with EVAP VSV switched off. If EVAP VSV operates as specified, go to step  17. If EVAP VSV does not operate as specified, go to next step.
    Fig 1: Testing EVAP VSV (Using Lexus Scan Tool)
    G00024241Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  14. Check for correct routing, damage, looseness and blockage in vacuum hoses between throttle body and EVAP VSV, and between EVAP VSV and charcoal canister. Repair as necessary. If vacuum hoses are okay, go to next step.
  15. Check EVAP VSV. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - GS300, GS430, IS300 & LS430 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.
  16. Check for open or short circuit in wiring harness and connector between EFI main relay, EVAP VSV and ECM. See WIRING DIAGRAMS article. Repair as necessary. If wiring harness is okay, replace ECM and retest.
  17. Turn ignition off. Disconnect canister closed valve VSV vacuum hoses. See Figure. 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 either port of canister closed valve VSV. Air should not flow from other port. Using scan tool, turn canister closed valve VSV off. Air should now flow from port. If VSV operates correctly, go to step  21. If VSV does not operate correctly, go to next step.
  18. Check vacuum hoses between canister closed 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.
  19. Check canister closed valve VSV. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - GS300, GS430, IS300 & LS430 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 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. See Figure. Disconnect vacuum hoses from pressure switching valve VSV. Using scan tool, activate pressure switching valve VSV. Apply compressed air to inner port of pressure switching valve VSV. Air should flow from outer port. Using scan tool, turn pressure switching valve VSV off. Air should no longer flow from outer port. 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 SYSTEM & COMPONENT TESTING - GS300, GS430, IS300 & LS430 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 WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest system.
  24. Backprobing ECM harness connector, connect DVOM between terminal No. 25 (Blue/Yellow wire) at ECM E5 connector and terminal No. 34 (Brown wire) at ECM E5 connector. See Figure. 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. 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. Backprobing ECM harness connector, connect DVOM between terminal No. 25 (Blue/Yellow wire) at ECM E5 connector and terminal No. 34 (Brown wire) at ECM E5 connector. See Figure. 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. 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 may be defective. Check fuel evaporation system. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - GS300, GS430, IS300 & LS430 article. Repair as necessary. If no problem is indicated, replace ECM.
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