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Home >> Mitsubishi >> 1994 >> Eclipse Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> Code 39: Oxygen Sensor (O2S)
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Code 39: Oxygen Sensor (O2S)

NOTE: For component terminal identification, see TERMINAL IDENTIFICATION  . For wiring diagrams, see WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.
  1. If using scan tester, go to step 3). Disconnect O2S connector. Install Test Harness (MB998464 ) between O2S and O2S connector. Using DVOM, check resistance between O2S connector terminals No. 1 and No. 3. O2S resistance should be 20 ohms at 68°F (20°C). If resistance is not as specified, replace O2S. If resistance is as specified, go to next step.
  2. Start and warm engine to operating temperature. Using jumper wires, ground O2S connector terminal No. 3 and apply 12 volts to O2S connector terminal No. 1. Using DVOM, check voltage between O2S connector terminals No. 2 and No. 4 while repeatedly racing engine. If voltage is not .6-1.0 volt, replace O2S. If voltage is as specified, go to step 5).
  3. Start and warm engine to operating temperature. Using scan tester, read O2S voltage. While monitoring scan tester, accelerate engine to 4000 RPM. Suddenly decelerate engine. Scan tester should read .2 volt or less. Suddenly accelerate engine. Scan tester should read .6-1.0 volt. If voltage is not as specified, replace O2S. If voltage is as specified, go to next step.
  4. While monitoring scan tester, accelerate to 2000 RPM and decelerate to 700 RPM (idle). Scan tester should switch between .6-1.0 volt and .4 volt or less. If voltage is not as specified, replace O2S. If voltage is as specified, go to next step.
  5. With O2S connector disconnected, turn ignition switch to ON position. Using DVOM, check voltage between chassis ground and O2S connector terminal No. 1. If system voltage does not exist, repair wiring harness as necessary. If system voltage exists, go to next step.
  6. Using DVOM, check for continuity between O2S connector terminal No. 4 and ECM connector terminal No. 56. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
  7. With O2S connector disconnected, check for continuity between chassis ground O2S connector terminal No. 2. If continuity does not exist, repair wiring harness as necessary. If continuity exists, condition required to set fault is not present at this time. Test is complete. Intermittent problem may exist. See TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
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