LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Eagle >> 1995 >> Vision ESi >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 3.3L >> Test TC-9A >> Left O2S Stays At Center (DTC 21)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Left O2S Stays At Center (DTC 21)

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION. For wiring diagram, see WIRING DIAGRAMS - 3.3L article in ENGINE PERFORMANCE. After each repair, perform TEST VER-2  .
NOTE: Scan tool displays left oxygen sensor as O2 and right oxygen sensor as O2R.
  1. Start engine. Using scan tool, read left Oxygen Sensor (O2S) voltage. If left O2S voltage is locked on 0.5 volt, go to step 5). If left O2S voltage is not locked on 0.5 volt, go to next step.
  2. Wiggle O2S wiring while observing scan tool display. If at any time O2S voltage locks on 0.5 volt when wiring is wiggled, repair harness or connector that caused voltage to lock (open circuit). If left O2S voltage does not lock on 0.5 volt when wiring is wiggled, go to next step.
  3. At this time, the condition required to set trouble code is not present. LEFT O2S STAYS AT CENTER trouble code sets if left 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: left O2S circuit open or left O2S failure. Go to next step.
  4. Inspect left O2S wiring and connectors. Repair wiring and connectors as required. If wiring and connectors are okay, see INACTIVE TROUBLE CODE CONDITION  . Test is complete.
  5. If left O2S is locked on 0.5 volt in step 1), disconnect left O2S connector. Using scan tool in ohmmeter mode, check resistance of O2S connector terminal No. 3 (Black/Light Blue wire). If resistance is more than 5 ohms, repair open Black/Light Blue wire. If resistance is less than 5 ohms, go to next step.
  6. Connect a jumper wire between left O2S connector terminal No. 2 (Black/Dark Green wire) and positive battery terminal. Using scan tool, read left O2S voltage. If voltage is more than one volt, replace left O2S. If voltage is less than one volt, go to next step.
  7. Turn ignition off. Disconnect Powertrain Control Module (PCM) connector. PCM is located under air cleaner. Leave jumper wire connected. Using scan tool in voltmeter mode, check voltage on PCM connector terminal No. 41 (Black/Dark Green wire). If voltage is more than 10 volts, replace PCM. If voltage is less than 10 volts, repair open Black/Dark Green wire.
scientia non olet · About LEMON Manuals