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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 27 (Engine Controls - Tests W/Codes - 3.0L) >> Self-Diagnostic Tests >> Test NTC-7A - Checking Oxygen Sensor (O2S) Switching

Test NTC-7A - Checking Oxygen Sensor (O2S) Switching

WARNING: This page is about a different car, the 1995 Plymouth Voyager, 1995 Plymouth Grand Voyager, 1995 Dodge Grand Caravan, and 1995 Dodge Caravan. However, it is still accessible from the selected car via links, so may be relevant.
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 O2S state. If O2S state is switching, system is functioning okay. Test is complete. If O2S state is not switching, check if O2S is locked on lean. If O2S is locked on lean, go to TEST NTC-7B. If 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 injectors or "O" rings 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-14A.
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