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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 TC-8A - O2S Stays At Center (DTC 21)

Test TC-8A - O2S Stays At Center (DTC 21)

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.
NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION  . For wiring diagrams, see WIRING DIAGRAMS  section.
  1. Start engine. Allow engine to reach normal operating temperature. Using scan tool, set engine speed to 1500 RPM. Using scan tool, read O2S state. If O2S is switching from rich to lean, go to next step. If O2S is not switching from rich to lean, go to step 5).
  2. While monitoring scan tool display, wiggle O2S connector and harness. If O2S locks on center, repair open harness or connector where wiggling caused O2S to stay at center. Perform TEST VER-2. If O2S is not locked on center, go to next step.
  3. At this time, condition required to set DTC is not present. O2S STAYS AT CENTER DTC sets if O2S output voltage stays at 0.5 volt for 1.5 minutes with engine temperature more than 170°F (76.6°C) and engine running for 2 minutes. Possible causes are: open O2S Dark Green/White wire or O2S failure. Go to next step.
  4. Inspect O2S wiring and connectors. Repair wiring and connectors as required. Perform TEST VER-2. If wiring and connectors are okay, test is complete. Perform TEST VER-2.
  5. Disconnect O2S connector. Using scan tool in ohmmeter mode, check resistance of O2S connector Black/Light Blue wire. If resistance is more than 5 ohms, repair open Black/Light Blue wire. Perform TEST VER-2. If resistance is less than 5 ohms, go to next step.
  6. Connect a jumper wire between O2S connector Dark Green/White wire and positive battery terminal. Using scan tool, read O2S voltage value. If voltage is more than one volt, replace O2S. Perform TEST VER-2. If voltage is less than one volt, go to next step.
  7. Turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Disconnect jumper wire. Using an external ohmmeter, check resistance of Dark Green/White wire between O2S connector and PCM connector terminal No. 41.
  8. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-2. If resistance is more than 5 ohms, repair open Dark Green/White wire. Perform TEST VER-2.
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