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Home › Dodge and Ram › 1995 › Spirit 2.5 K › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes - 2.5L Flex Fuel › Test TC-7A › O2S Stays At Center (DTC 21)

O2S Stays At Center (DTC 21)

NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION. For wiring diagrams, see WIRING DIAGRAMS - 2.5L FLEXIBLE FUEL 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 oxygen sensor (O2S) state. If O2S is locked at center, go to step 4). If O2S is not locked at center, wiggle oxygen sensor connector and wiring harness while watching scan tool display.
  2. If O2S was locked at center at any time, inspect all related wiring and connectors and repair as necessary. Perform TEST VER-2. If O2S was not locked at center at any time, condition required to set trouble code is not present at this time. The O2S STAYS AT CENTER trouble code sets if O2S output voltage stays at .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.
  3. Inspect all related wiring and connectors and repair as necessary. Perform TEST VER-2. If no problems were found with wiring and connectors, see INACTIVE TROUBLE CODE CONDITION. Perform TEST VER-2.
  4. Disconnect O2S connector. Put scan tool in ohmmeter mode. Using scan tool, check resistance of Black/Light Blue wire at O2S connector harness side. If resistance is more than 5 ohms, repair open in Black/Light Blue wire. Perform TEST VER-2.
  5. If resistance is less than 5 ohms, connect a jumper wire between O2S Black/Dark Green wire and battery positive terminal. Using scan tool, read O2S voltage. If voltage is more than one volt, replace O2S. Perform TEST VER-2.
  6. If O2S voltage is less than one volt, turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Disconnect jumper wire between O2S Black/Dark Green wire and battery positive terminal.
  7. Using an external ohmmeter, check resistance of O2S 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 in Black/Dark Green wire. Perform TEST VER-2.
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