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V6 Idle Mixture: 300ZX

  1. Start engine and warm to normal operating temperature. Perform self-diagnostics. See G - TESTS W/ CODES article in the ENGINE PERFORMANCE section.
  2. Ensure idle speed and ignition timing are correct. Locate ECM. See ECM LOCATIONS  table under 4-CYLINDER IDLE MIXTURE. Increase engine speed to 2000 RPM for another 2 minutes.
  3. Enter and set self-diagnostic system to Mode II. See appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section. Ensure Red LED on ECM goes on and off more than 5 times during a 10 second period with engine running at 2000 RPM. If LED does not turn on and off as specified, replace left oxygen sensor and repeat idle mixture procedure. If Red LED does not come on at all, go to step 7). If Red LED operates as stated, go to next step.
    NOTE: If idle mixture is still incorrect (Red LED on ECM does not go on and off more than 5 times during a 10 second period) after replacing left oxygen sensor, perform self-diagnostic procedure. Also check fuel pressure, airflow meter, injectors and engine coolant temperature sensor.
  4. Increase engine speed to 2000 RPM, 2 or 3 times. Red LED on ECM should go on and off more than 5 times during a 10 second period with engine running at 2000 RPM. If LED does not turn on and off as specified, replace right oxygen sensor and repeat test procedure starting at step 3). If Red LED does not come on at all, go to next step. If Red LED operates as stated, oxygen sensors and idle mixture are correct.
  5. Turn ignition off. Disconnect negative battery cable. To check right oxygen sensor, disconnect wiring harness connector. Disconnect ECM 76-pin connector.
  6. Check continuity between terminal No. 29 of ECM 76-pin connector and center terminal of oxygen sensor wiring harness connector. If continuity exists, go to step 9). If continuity does not exist, repair wiring harness and repeat idle mixture procedure starting at step 3).
  7. Turn ignition off. Disconnect negative battery cable. To check left oxygen sensor, disconnect wiring harness connector. Disconnect ECM 76-pin connector. Check continuity between terminal No. 55 of ECM 76-pin connector and center terminal of oxygen sensor wiring harness connector.
  8. If continuity exists, go to next step. If continuity does not exist, repair wiring harness and repeat idle mixture procedure starting at step 3).
  9. Reconnect ECM 76-pin connector. Disconnect engine coolant temperature sensor connector. Connect a 2500-ohm resistor to engine coolant temperature sensor wiring harness.
  10. Reconnect negative battery cable. Start engine and warm to normal operating temperature (coolant gauge needle in middle). Increase engine speed to 2000 RPM, 2 or 3 times, then allow engine to return to idle.
  11. Check idle mixture (CO% level). See V6 IDLE SPEED & CO% LEVEL  table under V6 IDLE SPEED. If idle mixture (CO% level) is correct, replace right oxygen sensor and repeat procedure starting at step 3).
  12. If idle mixture (CO% level) is incorrect, reconnect oxygen sensor. Perform self-diagnostics. See G - TESTS W/ CODES article in the ENGINE PERFORMANCE section. Service all fault codes. If no fault codes are present, check fuel pressure, airflow meter, injectors and engine coolant temperature sensor for faults. If all systems are operating correctly but idle CO% level is still incorrect, replace ECM.
Fig 1: ECM Conn. Terminal ID - As Viewed From Wiring Harness Side (Altima, NX, Pathfinder, Pickup, Sentra, Quest & 240SX)
G50D05612Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 2: ECM Conn. Terminal ID - As Viewed From Wiring Harness Side (Maxima & 300ZX)
G50F05613Courtesy of NISSAN MOTOR CO., U.S.A.
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