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Home >> Mitsubishi >> 1993 >> Eclipse Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> Code 39: Oxygen (O2) Sensor
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Code 39: Oxygen (O2) Sensor

NOTE: For component terminal identification, see TERMINAL IDENTIFICATION  . For wiring diagrams, see WIRING DIAGRAMS article in this section.
  1. If using scan tester, go to step 3. Disconnect O2 sensor connector. Install Test Harness (MB998464 ) between O2 sensor and O2 sensor connector. Using DVOM, check resistance between O2 sensor connector terminals No. 1 and 3. O2 sensor resistance should be 20 ohms at 68°F (20°C). If resistance is not as specified, replace O2 sensor. If resistance is as specified, go to next step.
  2. Start and warm engine to operating temperature. Using jumper wires, ground O2 sensor connector terminal No. 3 and apply 12 volts to O2 sensor connector terminal No. 1. Using DVOM, check voltage between O2 sensor connector terminals No. 2 and 4 while repeatedly racing engine. If voltage is not .6-1.0 volt, replace O2 sensor. If voltage is as specified, go to step 5.
  3. Start and warm engine to operating temperature. Using scan tester, read O2 sensor voltage. While monitoring scan tester, accelerate to 4000 RPM. Suddenly decelerate. Scan tester should read .2 volt or less. Suddenly accelerate. Scan tester should read .6-1.0 volt. If voltage is not as specified, replace O2 sensor. 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 O2 sensor. If voltage is as specified, go to next step.
  5. With O2 sensor connector disconnected, turn ignition switch to ON position. Using DVOM, check voltage between chassis ground and O2 sensor 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 O2 sensor 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 O2 sensor connector disconnected, check for continuity between chassis ground O2 sensor 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 this section.
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