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Diagnosis & Repair (Using OBD-II Scan Tool)

WARNING: This page is about a different car, the 2002 Lexus RX 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 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. See Figure.
  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. See Figure.
  10. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals No. 2 (Yellow/Black wire) and No. 18 (Brown wire) at ECM E8 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 (66.7 kPa) to vapor pressure sensor.
  11. Locate vapor pressure sensor on top of fuel tank. See Figure. Leaving harness connector attached, remove vapor pressure sensor from top of fuel tank. See Figure. Backprobing ECM harness connectors, connect voltmeter between terminal No. 17 (Blue/Orange wire) at ECM E5 connector and terminal No. 18 (Brown wire) at ECM E8 connector. See Figure. Connect a vacuum pump to vapor port on sensor. Voltage should be 2.9-3.7 volts without vacuum applied, and .5 volts or less with 1.18 in. Hg (4.0 kPa) applied. 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. Access ECM harness connectors behind glove box. Backprobing connector, connect a fused jumper wire between ground and terminal No. 7 (White/Blue wire) at ECM E8 connector. See Figure. 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  16. 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
  14. Check EVAP VSV operation. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If EVAP VSV is okay, go to next step. If EVAP VSV is not okay, replace EVAP VSV. 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.
  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. VSV is mounted on air filter housing. See Figure. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing connector, connect a fused jumper wire between ground and terminal No. 10 (Green wire) at ECM E5 connector. See Figure. Apply compressed air to VSV port "B". See Figure. Air should not flow from VSV port "A". Disconnect fused jumper wire. Air should flow from port "A". 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 valve VSV and charcoal canister. Also clean vacuum hose between charcoal canister and closed canister valve VSV.
  18. Check for an open or short in wiring harness between EFI main relay, closed canister 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 harness connectors behind glove box. Backprobing connector, connect a fused jumper wire between ground and terminal No. 3 (Blue/Red wire) at ECM E6 connector. See Figure. Disconnect pressure switching valve VSV vacuum hoses. VSV is located on charcoal canister. See Figure. 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  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. If no problem is indicated, replace ECM.
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