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Test TC-129A - Downstream O2 Sensor Stays At Center

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION  Directory. For wiring diagram, see appropriate WIRING DIAGRAMS - NON-TURBO article.
NOTE: 2.0L is equipped with one upstream O2 sensor.
  1. Start engine. Allow engine to reach normal operating temperature. Using scan tool, set engine speed to 1500 RPM. Using scan tool, read downstream O2 sensor state. If downstream O2 sensor state is switching once every 10 seconds, go to next step. If downstream O2 sensor state is not switching once every 10 seconds, go to step 5).
  2. While monitoring scan tool display, wiggle downstream O2 sensor wiring harness. If downstream O2 sensor state locked at center at any time, repair wiring harness as necessary where wiggling caused problem to appear. Perform TEST VER-5A. If downstream O2 sensor state did not lock at center at any time, go to next step.
  3. Condition to set trouble code is not present at this time. DOWNSTREAM O2 SENSOR STAYS AT CENTER DTC sets if downstream O2 sensor signal voltage stays .39-.52 volt during the trip. PCM pulls sensor voltage to 5 volts for 30 seconds and monitors sensor voltage. If voltage stays at 5 volts, this DTC will set indicating no activities. Possible causes are:
    • O2 sensor output wire open
    • O2 sensor ground circuit open
    • O2 sensor failure
    • Powertrain Control Module (PCM) failure.
  4. Inspect all related wiring and connectors and repair as necessary. If no problems were found with wiring and connectors, see INACTIVE TROUBLE CODE CONDITION . Test is complete. Perform TEST VER-5A. If related wiring and connectors were repaired, perform TEST VER-5A.
  5. Turn ign. Disconnect downstream O2 sensor connector. Using scan tool in ohmmeter mode, check resistance of O2 sensor connector sensor ground circuit (harness side). See the DOWNSTREAM O2 SENSOR CONNECTOR WIRE ID (HARNESS SIDE) . If resistance is 5 ohms or less, go to next step. If resistance is more than 5 ohms, repair open to sensor ground circuit. See the DOWNSTREAM O2 SENSOR CONNECTOR WIRE ID (HARNESS SIDE). Perform TEST VER-5A.
  6. Connect a jumper wire between downstream O2 sensor connector (harness side) between signal circuit and battery positive terminal. See DOWNSTREAM O2 SENSOR CONNECTOR WIRE ID  (HARNESS SIDE). Using scan tool, read downstream O2 sensor voltage. If voltage is one volt or less, go to next step. If voltage is more than one volt, replace downstream O2 sensor. Perform TEST VER-5A.
  7. Disconnect jumper wire. Turn ignition off. Disconnect Powertrain Control Module connector. Using an external ohmmeter, check resistance of downstream O2 sensor signal circuit between O2 sensor connector (harness side) and PCM connector terminal No. 51. See DOWNSTREAM O2 SENSOR CONNECTOR WIRE ID (HARNESS SIDE)  for wire color identification. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-5A. If resistance is 5 ohms or more, repair open downstream O2 sensor signal circuit. Perform TEST VER-5A.
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