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Closed Loop Test

NOTE: Voltmeter used in tests must have a minimum impedance of 10 meg-ohms per volt.
  1. With engine "OFF", remove air cleaner and plug vacuum hoses. Turn ignition "ON" for 4 seconds, then turn "OFF". Disconnect stepper motor and oxygen sensor connectors.
  2. Connect positive lead of voltmeter to terminal 2 and negative lead to terminal 4 of oxygen sensor connector (sensor side). Set voltmeter to 1 volt scale.
  3. Start engine and warm for 4 minutes. Increase engine speed to 1200 RPM while closing choke valve. Run engine, with valve closed, for 1 minute. While choke is closed, voltmeter should indicate a minimum of 0.6 volts. Turn ignition switch "OFF". If okay, replace MCU and proceed to step  5. If not okay, continue to step 4)  .
  4. Disconnect and plug hose leading to air distribution check valve at exhaust manifold. Repeat step 3)  . If okay, replace air distribution check valve and continue. If not okay, replace the oxygen sensor and continue.
  5. Unplug and reconnect air distribution check valve hose. Remove voltmeter and reconnect harness connectors. Install air cleaner.
    NOTE: If after completing Closed Loop Check and Test, the problem still exists, recheck for other engine malfunctions that can effect air/fuel mixture, combustion efficiency and exhaust gas composition.
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