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Diagnosis & Repair (Using OBD-II Scan Tool)

WARNING: This page is about a different car, the 2002 Lexus GS 430. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check for cracks, deformations or loose connections in 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. Turn ignition on. Backprobing, measure voltage between terminals No. 27 (Blue/Red wire) and No. 26 (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.
    NOTE: DO NOT apply more than 19.7 in. Hg of vacuum to vapor pressure sensor.
  11. Backprobing ECM harness connector, measure voltage between terminals No. 25 (Blue/Yellow wire) and No. 26 (Brown wire) at ECM E5 connector. Disconnect vacuum supply hose (hose closest to electrical connector) from vapor pressure sensor. Sensor is mounted on charcoal canister and is located next to fuel tank. 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 in. Hg of vacuum applied, go to step  13. If voltage is not as specified, go to next step.
  12. Check for an open or short circuit in wiring harness and connector between vapor pressure sensor and ECM. See WIRING DIAGRAMS article. Repair as necessary. If wiring harness and connector are okay, replace vapor pressure sensor and retest.
  13. Turn ignition on. Disconnect EVAP VSV vacuum hoses. VSV is located on top of air intake chamber, near PCV valve. Backprobing, connect fused jumper wire between ground and terminal No. 11 (Green/Black wire) at ECM E2 connector. Apply compressed air to EVAP VSV port "E". See Fig 1. Air should flow from port "F". Disconnect fused jumper wire. Air should not flow from port "F". If EVAP VSV does not function as specified, go to next step. If EVAP VSV functions as specified, go to step  16.
    Fig 1: Testing EVAP VSV
    G00024254Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  14. Remove EVAP VSV. Using ohmmeter, measure resistance between VSV terminals. With VSV temperature at 68°F (20°C), resistance should be 30-34 ohms. Measure resistance between each terminal and body of valve. Resistance should be infinite. If resistance is as specified, using fused jumper wires, apply battery voltage and ground to EVAP VSV terminals. Apply compressed air to EVAP VSV port "E". Air should flow from port "F". See Fig 1. Disconnect fused jumper wires. Air should not flow from port "F". If EVAP VSV does not operate as specified, or if resistance was not as specified, replace EVAP VSV and charcoal canister. After replacing components, clean vacuum hoses between EVAP VSV and throttle body, and between EVAP VSV and charcoal canister. If EVAP VSV operates as specified, go to next step.
  15. 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.
  16. Turn ignition off. Disconnect canister closed valve VSV vacuum hose. VSV is mounted on back of intake air baffle and has a Black 2-pin connector with White and Yellow wires. Access ECM under protective cover, behind left headlight in engine compartment. Turn ignition on. Backprobing, connect a fused jumper wire between ground and terminal No. 22 (Yellow wire) at ECM E4 connector. See Figure. Air should not flow through canister closed valve VSV. Disconnect fused jumper wire. Air should flow through canister closed valve VSV. 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 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.
  18. Check for an open or short circuit 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. Access ECM under protective cover, behind left headlight in engine compartment. Backprobing, connect a fused jumper wire between ground and terminal No. 10 (White/Red wire) at ECM E5 connector. See Figure. Locate pressure switching valve VSV on charcoal canister, mounted next to tank. Pressure switching valve VSV has 2 vacuum ports and a Blue 2-pin connector with White/Red and Black/Red wires. Apply compressed air to port "E" of pressure switching valve VSV. Air should flow from port "F". See Figure. Remove fused jumper wire. Air should not flow from port "F". 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 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.
  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 appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary.
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