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Checking Oxygen Sensor (O2S) Switching

WARNING: High fuel pressure may be present in fuel lines. Open fuel system with caution. See FUEL PRESSURE RELEASE  procedure.
  1. Allow engine to reach normal operating temperature. Using scan tool, read both upstream oxygen sensor (O2S) states for 10 seconds. If both O2S states are switching between rich/lean, system is functioning okay. Test is complete. If both O2S states are not switching, check if upstream O2S is locked on lean. If upstream O2S is locked on lean, go to step 5). If upstream O2S is not locked on lean, turn engine off.
  2. Release fuel pressure. Install fuel pressure gauge in fuel supply line. Turn ignition on. Using scan tool, actuate fuel system. Allow fuel pressure gauge to stabilize to normal fuel pressure. Stop fuel system actuation. Monitor fuel pressure gauge for one minute.
  3. If fuel pressure gauge reading drops more than 10 psi (0.7 kg/cm2 ), replace leaking injector(s) as necessary. Perform TEST VER-2 . If fuel pressure gauge reading does not drop more than 10 psi (0.7 kg/cm2 ), go to next step.
  4. Inspect air cleaner and inlet ducts for restrictions. Repair as necessary. Perform TEST VER-2. If no restrictions are present, go to TEST NTC-18A .
  5. Turn ignition off. Tee in a vacuum gauge to a manifold vacuum source. Start engine and allow it to idle. Observe vacuum gauge for any abnormal vacuum conditions. If abnormal vacuum conditions are not observed, go to next step. if abnormal vacuum conditions are observed, repair engine for mechanical failure as necessary. Perform TEST VER-1 .
  6. Using scan tool, observe faulty upstream O2S voltage signal. If voltage is more than .10 volt, go to step 9). If voltage is less than .10 volt, turn ignition off. Disconnect faulty upstream O2S connector. See Fig 1, Fig 2, Fig 3 and Fig 4 .
    Fig 1: Locating Front Upstream O2S (FJ22 Body)
    G95G12662
    Fig 2: Locating Front Upstream O2S (JA Body)
    G95I12664
    Fig 3: Locating Rear Upstream O2S (FJ22 Body)
    G95H12663
    Fig 4: Locating Rear Upstream O2S (JA Body)
    G95J12665
  7. Disconnect faulty upstream O2S connector. Disconnect Powertrain Control Module (PCM) connector. Using scan tool in ohmmeter mode, check resistance of faulty upstream O2S connector signal circuit. See O2S SIGNAL CIRCUIT IDENTIFICATION table. Go to next step.
    O2S SIGNAL CIRCUIT IDENTIFICATION

    Application Wire Color
    FJ22 Body
    Front Upstream O2S White/Black
    Rear Upstream O2S Dark Green/Black
    JA Body
    Front Upstream O2S Black/Dark Green
    Rear Upstream O2S Tan/White
  8. If resistance is less than 5 ohms, repair short to ground in appropriate wire. Perform TEST VER-2. If resistance is more than 5 ohms, replace faulty upstream O2S. Perform TEST VER-2.
  9. Turn engine off. If faulty upstream O2S has not been replaced, replace faulty O2S. Go to next step. If faulty upstream O2S has been replaced, go to next step.
  10. Turn ignition on. Using scan tool, reset adaptive fuel memory. Start engine. Allow engine to reach normal operating temperature. Using scan tool, read upstream O2S state. If upstream O2S state is switching between rich/lean, repair is complete. Perform TEST VER-2 . If upstream O2S state is not switching between rich/lean, go to TEST NTC-18A .
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