LEMON Manuals: Even more car manuals for everyone
Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 35 (Engine Controls - Tests W/Codes - 3.9L) >> Self-Diagnostic Tests >> Test TC-8A - O2S Stays At Center Or Left O2S Stays At Center (DTC 21)

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

WARNING: This page is about a different car, the 1995 Dodge Ram Wagon, 1995 Dodge Ram Van, 1995 Dodge Pickup, 1995 Dodge Dakota, and 1995 Dodge Cab & Chassis. 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 diagram, see WIRING DIAGRAMS  section at the end of this article.
  1. Start engine. Allow engine to run until normal operating temperature is reached. Using scan tool, set engine speed to 1500 RPM. Using scan tool, read O2S state.
  2. If O2S is not switching from rich to lean, go to step 7). If O2S is switching from rich to lean, wiggle sensor connector and wiring harness while watching scan tool display.
  3. If O2S stopped switching, inspect all related wiring, paying particular attention to O2S signal circuit (Black/Dark Green wire) and connectors. Repair as necessary. Perform TEST VER-2. If O2S did not stop switching, condition required to set trouble code is not present at this time. Go to next step.
  4. O2S STAYS AT CENTER trouble code sets if O2S output voltage stays at 0.5 volt for 1.5 minutes with engine temperature more than 170°F (77°C) and engine running for 2 minutes. Possible causes are: open O2S circuit or O2S failure. Go to next step.
  5. LEFT O2S STAYS AT CENTER trouble code sets if O2S signal voltage is more than 4.8 volts with engine temperature more than 170°F (77°C) and engine running for 2 minutes. Possible causes are: O2S failure, open O2S signal circuit or open O2S ground circuit. Go to next step.
  6. Inspect all related wiring and connectors. Repair as necessary. Perform TEST VER-2. If no problems are found with wiring and connectors, test is complete. Perform TEST VER-2.
    NOTE: When performing steps 7)-10) on dual O2S systems, disconnect left O2S connector.
  7. Turn ignition off. Disconnect O2S connector (on dual O2S system, disconnect left O2S connector). Turn ignition on. Using scan tool in voltmeter mode, check voltage on O2S signal circuit (Black/Dark Green wire) at O2S connector harness side. If voltage is less than 10 volts, go to next step. If voltage is more than 10 volts, repair appropriate wire for a short to voltage. Perform TEST VER-2.
  8. Turn ignition off. Using scan tool in ohmmeter mode, check resistance of O2S ground circuit (Black/Light Blue wire) at O2S connector harness side. If resistance is more than 5 ohms, repair open Black/Light Blue wire. Perform TEST VER-2.
  9. If resistance is less than 5 ohms, connect a jumper wire between O2S signal circuit (Black/Dark Green wire) at O2S connector harness side and ground. Using scan tool, read O2S voltage. If O2S voltage is less than 0.2 volt, replace O2S. Perform TEST VER-2.
  10. If O2S voltage is more than 0.2 volt, disconnect jumper wire. Turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Using an external ohmmeter, check resistance of O2S signal circuit (Black/Dark Green wire) between O2S connector harness side and PCM connector terminal No. 41. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-2. If resistance is more than 5 ohms, repair open O2S signal circuit. Perform TEST VER-2.
scientia non olet · About LEMON Manuals