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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 43 (Engine Controls - Tests W/Codes - 8.0L) >> Self-Diagnostic Tests >> Test NTC-7A - Checking O2S Switching

Test NTC-7A - Checking O2S Switching

WARNING: This page is about a different car, the 1995 Dodge Pickup and 1995 Dodge Cab & Chassis. 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.
NOTE: Scan tool displays dual O2S as LT O2S and RT O2S.
  1. Allow engine to reach normal operating temperature. Using scan tool, read RT O2S voltage. Raise engine speed to more than 1500 RPM. If RT O2S voltage is switching from less than 0.4 volt to more than 0.6 volt, go to TEST NTC-7B. If voltage is not switching as specified, go to next step.
  2. If RT O2S voltage stays less than 0.4 volt, go to step 5). If RT O2S voltage does not stay less than 0.4 volt, turn engine off. Release fuel pressure. Install a fuel pressure gauge to fuel rail test port. Turn ignition on. Using scan tool, actuate fuel system. Allow fuel pressure to stabilize. Go to next step.
  3. Stop fuel system actuation. Monitor fuel gauge for one minute. If fuel pressure drops to less than 25 psi (1.8 kg/cm2 ), replace leaking injector(s) as necessary. Perform TEST VER-2.
  4. If fuel pressure does not drop to less than 25 psi (1.8 kg/cm2 ), inspect air filter and air inlet ducts for restrictions. Clean restricted air inlet system as necessary. Perform TEST VER-2. If no restrictions exist, go to TEST NTC-18A.
  5. Allow engine to idle. Inspect engine for abnormal vacuum conditions. Repair abnormal vacuum conditions as necessary. Perform TEST VER-2. If no abnormal vacuum conditions exist, go to next step.
  6. Using scan tool, read RT O2S voltage. If RT O2S voltage does not stay less than 0.1 volt, go to step 8). If RT O2S voltage stays less than 0.1 volt, turn ignition off. Disconnect right O2S connector. Go to next step.
  7. Disconnect Powertrain Control Module (PCM) connector. Using scan tool in ohmmeter mode, check resistance of PCM connector terminal No. 41, right O2S signal circuit (Black/Dark Green wire). If resistance is less than 5 ohms, repair short to ground in Black/Dark Green wire. Perform TEST VER-2. If resistance is more than 5 ohms, replace right O2S. Perform TEST VER-2.
  8. Turn engine off. Replace right O2S. Turn ignition on. Using scan tool, reset adaptive fuel memory. Start engine. Allow engine to reach operating temperature. Using scan tool, read RT O2S voltage. If RT O2S voltage is switching between less than 0.4 volt and more than 0.6 volt, repair is complete. Perform TEST VER-2. If RT O2S voltage is not switching as specified, reconnect right O2S connector. Go to TEST NTC-18A.
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