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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 TC-9A - Right O2S Stays At Center (DTC 21)

Test TC-9A - Right O2S Stays At Center (DTC 21)

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.
NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION  . For wiring diagrams, see WIRING DIAGRAMS  section at the end of this article.
NOTE: Scan tool displays dual O2S as LT O2S and RT O2S.
  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 RT O2S voltage.
  2. If voltage is not switching from less than 0.4 volt to more than 0.6 volt, go to step 6). If voltage is switching from less 0.4 volt to more than 0.6 volt, wiggle left O2S connector and wiring harness while watching scan tool display.
  3. If right O2S voltage goes more than 4.8 volts at any time, repair open harness or connector causing voltage change. Perform TEST VER-2. If sensor voltage does not go more than 4.8 volts at any time, condition required to set trouble code is not present at this time. Go to next step.
  4. RIGHT O2S STAYS AT CENTER trouble code sets if O2S output voltage is more than 4.8 volts with engine temperature more than 176°F (80°C) and engine running for 2 minutes. Possible causes are: open right O2S signal circuit (Black/Dark Green wire), open right O2S ground circuit (Black/Light Blue wire), right O2S failure, faulty wiring or faulty connectors. Go to next step.
  5. 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.
  6. Turn engine off. Disconnect right O2S connector. Turn ignition on. Using scan tool in voltmeter mode, check voltage on right O2S connector, signal circuit (Black/Dark Green wire). If voltage is more than 10 volts, repair short to voltage in Black/Dark Green wire. Perform TEST VER-2.
  7. If voltage is less than 10 volts, turn ignition off. Using scan tool in ohmmeter mode, check resistance of right O2S connector, ground circuit (Black/Light Blue wire). If resistance is more than 5 ohms, repair open Black/Light Blue wire. Perform TEST VER-2.
  8. If resistance is less than 5 ohms, connect a jumper wire between right O2S signal circuit (Black/Dark Green wire) and engine ground. Using scan tool, read RT O2S voltage. If O2S voltage is less than 0.2 volt, replace right O2S. Perform TEST VER-2.
  9. If O2S voltage is more than 0.2 volt, turn ignition off. Disconnect jumper wire. Disconnect Powertrain Control Module (PCM) connector. Using an external ohmmeter, check resistance of right O2S signal circuit (Black/Dark Green wire) between right O2S connector 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 Black/Dark Green wire. Perform TEST VER-2.
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