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Home >> Lexus >> 1999 >> SC 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Emission Systems & Sub-Systems >> Fuel Evaporation System (SC300 & SC400) >> Vapor Pressure Sensor Circuit

Vapor Pressure Sensor Circuit

  1. Disconnect vapor pressure sensor connector. Sensor has one vacuum port and is mounted on top of EVAP charcoal canister at right front of engine compartment. See Figure. Measure voltage between terminals VC (Blue/Black wire) and E2 (Brown wire) at vapor pressure sensor connector terminals. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, check wiring harness between sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM.
  2. Turn ignition off. Reconnect vapor pressure sensor connector. Access ECM connectors under front of carpet on passenger side of vehicle. Disconnect vapor pressure sensor vacuum hose. Turn ignition on. Backprobing ECM connector, measure voltage between terminals No. 18 (Brown wire) and No. 2 (Blue/Black wire) at ECM E16 connector. See Figure. Voltage reading should be as follows:
    • 3.0-3.6 volts with no vacuum applied.
    • 1.3-2.1 volts with .59 in. Hg (2.0 kPa) of vacuum applied.
    • 4.2-4.8 volts with .22 psi (1.5 kPa) of pressure applied.

    If voltage is not as specified, replace vapor pressure sensor.

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