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Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Check EVAP VSV, vapor pressure sensor VSV and vapor pressure sensor connectors for damaged pins, corrosion and loose wires. For component locations, see appropriate illustration in THEORY & OPERATION article. If problem exists, repair connectors as necessary. If problem does not exist, go to next step.
  2. Check all EVAP related vacuum hoses for cracks, looseness and correct routing. For proper vacuum hose routing, see appropriate illustration in VACUUM DIAGRAMS article. If problem exists, repair vacuum hoses as necessary. If problem does not exist, go to next step.
  3. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM harness connector and measure voltage between terminals No. 2 (Blue/Red wire) and No. 18 (Brown wire) at ECM harness connector E7. See Figure. If voltage is not 4.5-5.5 volts, replace ECM. If voltage is 4.5-5.5 volts, go to next step.
  4. Using DVOM, backprobe ECM harness connector and measure voltage between terminal No. 17 (Pink wire) at ECM harness connector E12 and terminal No. 18 (Brown wire) at ECM harness connector E7. See Figure. Disconnect vacuum hose from vapor pressure sensor. Vapor pressure sensor is mounted on firewall, near brake booster. Connect a vacuum pump to vapor pressure sensor. Voltage should be 2.9-3.7 volts without vacuum applied and .5 volt or less with 1.8 in. Hg applied. If voltage is as specified, go to step  6. If voltage is not as specified, go to next step.
  5. Check for open or short in wiring between vapor pressure sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace vapor pressure sensor.
  6. Disconnect EVAP VSV vacuum hoses. EVAP VSV is located on front top of engine. Apply air pressure to EVAP VSV port "E". See Fig 1. Air should not flow from port "F". Access ECM behind glove box. Turn ignition on. Using a jumper wire, backprobe between ground and terminal No. 7 (Black/Red wire) at ECM harness connector E7. See Figure. Air should flow from port "F". If EVAP VSV operates as specified, go to step  10. If EVAP VSV does not operate as specified, go to next step.
  7. Check vacuum hose between intake manifold and EVAP VSV, and hose between EVAP VSV and charcoal canister. If problem exists, replace vacuum hoses as necessary. If problem does not exist, go to next step.
  8. Check EVAP VSV. See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. If problem exists, replace EVAP VSV. If problem does not exist, go to next step.
  9. Check for open or short in wiring between EFI main relay, EVAP VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace ECM.
  10. Disconnect vapor pressure sensor VSV vacuum hoses. Vapor pressure sensor VSV is mounted on top of EVAP charcoal canister on left side of engine compartment. Apply air pressure to vapor pressure sensor VSV port "E". See Figure. Air should flow from port "G". Access ECM behind glove box. Turn ignition on. Using a jumper wire, backprobe between ground and terminal No. 9 (White/Blue wire) at ECM harness connector E12. See Figure. Air should flow from port "F". If vapor pressure sensor VSV does not operate as specified, go to next step. If vapor pressure sensor VSV operates as specified, check charcoal canister. Perform appropriate fuel EVAP system test. See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article.
  11. Check vapor pressure sensor VSV. See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. If problem exists, replace vapor pressure sensor VSV. If problem does not exist, go to next step.
  12. Check for open or short in wiring between EFI main relay, vapor pressure sensor VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. If problem exists, repair wiring harness as necessary. If problem does not exist, replace ECM.
Fig 1: Identifying EVAP Vacuum Switching Valve (VSV) Ports
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