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Home >> Lexus >> 1999 >> SC 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - Tests >> Diagnostic Tests >> DTC P0441: Incorrect EVAP Purge Flow Or DTC P0446: EVAP Vent Control Fault >> Diagnosis & Repair (Using OBD-II Scan Tool)

Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Check for loose or disconnected connectors at EVAP VSV, vapor pressure sensor VSV and vapor pressure sensor. Repair as necessary. If all connectors are okay, go to next step.
  2. Check for correct routing, damage, looseness and blockage in vacuum hoses between vapor pressure sensor and vapor pressure sensor VSV, and between vapor pressure sensor VSV and charcoal canister. Also check vacuum hoses between EVAP VSV and charcoal canister, between EVAP VSV and air resonator, and between intake manifold and charcoal canister. Repair as necessary. If vacuum hoses are okay, go to next step.
  3. Turn ignition on. Backprobing, measure voltage between terminals No. 2 (Blue/Black wire) and No. 18 (Brown wire) at ECM E16 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.
  4. Backprobing, measure voltage between terminal No. 22 (Red wire) at ECM E18 connector and terminal No. 18 (Brown wire) at ECM E16 connector. See Figure. Disconnect vacuum hose from vapor pressure sensor. Vapor pressure sensor is mounted on charcoal canister at right front of vehicle. Connect a vacuum pump to sensor. If voltage is 2.9-3.7 volts without vacuum applied, and .5 volt or less with 1.2-19.7 in. applied, go to step  6. If voltage is not as specified, go to next step.
  5. Check for an open or short circuit in wiring harness and connector between vapor pressure sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring harness and connector are okay, replace vapor pressure sensor and retest.
  6. Turn ignition on. Backprobing, connect fused jumper wire between ground and terminal No. 7 (Green/Red wire) at ECM E16 connector. Apply compressed air to EVAP VSV port "E". Air should flow from port "F". Disconnect fused jumper wire. Air should not 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. Remove engine cover. 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, go to next step. If resistance is not as specified, replace EVAP VSV and charcoal canister. After replacing components, clean vacuum hoses between throttle body and EVAP VSV, and between EVAP VSV and charcoal canister.
  8. 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, 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.
  9. Check for open or short circuit in wiring harness and connector between EFI main relay, EVAP VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring harness is okay, replace ECM and retest.
  10. Turn ignition on. Backprobing ECM harness connector, connect fused jumper wire between ground and terminal No. 10 (White/Blue wire) at ECM E18 connector. See Figure. Apply compressed air to vapor pressure sensor VSV port "E". Air should flow from port "F". See Fig 2. Disconnect fused jumper wire. Air should flow from port "G". If vapor pressure sensor VSV functions as specified, go to next step. If vapor pressure sensor VSV does not function as specified, go to step  15.
  11. Remove charcoal canister. Visually inspect charcoal canister for cracks or damage. Close "B" port of charcoal canister. See Fig 3. Apply .26 psi (.02 kg/cm2 ) of compressed air to "A" port of charcoal canister. Air should flow from "D" port.
  12. Close "B" and "D" port. See Fig 3. Apply .26 psi (.02 kg/cm2 ) of compressed air to "A" port of charcoal canister. Air should not flow from "C" port.
  13. Apply 1.01 in. Hg of vacuum to "B" port. See Fig 3. Vacuum should not decrease with "C" port closed and should decrease with "C" port open.
  14. Close "C" port. See Fig 3. Connect vacuum gauge to "B" port. Apply .29 in. Hg of vacuum to "A" port. Vacuum should exist at "B" port. If charcoal canister does not operate as specified, replace as necessary. If charcoal canister is okay, replace ECM and retest.
  15. Remove vapor pressure sensor VSV. Using ohmmeter, measure resistance between vapor pressure sensor VSV terminals. With vapor pressure sensor VSV temperature at 68°F (20°C), resistance should be 37-44 ohms. Measure resistance between each terminal and body of valve. Resistance should be infinite.
  16. If resistance is not as specified, replace vapor pressure sensor VSV and charcoal canister. After replacing components, clean vacuum hoses between vapor pressure sensor VSV and vapor pressure sensor, and between vapor pressure sensor VSV and charcoal canister. If resistance is as specified, go to next step.
  17. Using fused jumper wires, apply battery voltage and ground to vapor pressure sensor VSV terminals. Apply compressed air to vapor pressure sensor VSV port "E". Air should flow from port "F". See Fig 2. Disconnect fused jumper wires. Air should flow from port "G". If vapor pressure sensor VSV operates as specified, go to step  19.
  18. If vapor pressure sensor VSV does not operate as specified, replace vapor pressure sensor VSV and charcoal canister. After replacing components, clean vacuum hoses between vapor pressure sensor VSV and vapor pressure sensor, and between vapor pressure sensor VSV and charcoal canister.
  19. Check for open or short circuit in wiring harness and connectors between EFI main relay, vapor pressure sensor VSV and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring harness is okay, replace ECM and retest.
Fig 1: Identifying EVAP VSV Vacuum Ports
G96D09634Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 2: Identifying Vapor Pressure Sensor VSV Vacuum Ports
G98G11540Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 3: Identifying Charcoal Canister Components
G98C11538Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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