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Diagnosis & Repair (Using OBD-II 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. 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. 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. See Figure. 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. See Figure. 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. Disconnect EVAP VSV vacuum hoses. See Figure. Turn ignition on. Backprobing, connect a fused jumper wire between ground and terminal No. 11 (Blue/Yellow wire) at ECM E2 connector. See Figure. Apply compressed air to inner EVAP VSV port. Air should flow from outer EVAP VSV port. Remove fused jumper wire. Air should not flow from outer EVAP VSV port. If EVAP VSV functions as specified, go to step  16. If EVAP VSV does not function as specified, go to next step.
  14. Check EVAP VSV operation. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - GS300, GS430, IS300 & LS430 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.
  15. Check for an open or short in wiring harness between EFI main relay, EVAP VSV and ECM. See WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest system.
  16. Disconnect canister closed valve VSV vacuum hoses. See Figure. Turn ignition on. Backprobing, connect a fused jumper wire between ground and terminal No. 22 (Black/Blue wire) at ECM E4 connector. See Figure. Apply compressed air to either VSV port. Air should not flow from other VSV port. Disconnect fused jumper wire. Air should now flow from other VSV port. If VSV does not function as specified, go to next step. If VSV functions as specified, go to step  19.
  17. Check canister closed valve VSV. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - GS300, GS430, IS300 & LS430 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.
  18. 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.
  19. Turn ignition on. Backprobing, connect a fused jumper wire between ground and terminal No. 13 at ECM E5 connector. See Figure. Disconnect pressure switching valve VSV vacuum hoses. VSV is located on charcoal canister. Apply compressed air to one VSV port. Air should flow from other VSV port. Remove fused jumper wire. Air should no longer flow from other port. If VSV functions as specified, go to step  22. If VSV does not function as specified, go to next step.
  20. 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.
  21. 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.
  22. 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.
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