Test NF-6A - Checking Oxygen (O2) Sensor Switching

Allow engine to reach normal operating temperature. Using DRB-II, read O2 sensor state. If O2 sensor state is switching, system is functioning okay. If O2 sensor state is not switching and locked on lean, perform TEST NF-6B. If O2 sensor is not locked on lean, turn engine off.
Let engine cool for 5 minutes. Remove and inspect spark plugs for wet tips or fuel fouling. If either condition exists, replace leaking injectors at corresponding cylinders. Perform VERIFICATION PROCEDURE VER-3.
If neither condition exists, inspect air cleaner and air inlet ducts for restrictions. Clean restricted air inlet as necessary. Perform VERIFICATION PROCEDURE VER-3. If air inlet is not restricted, perform TEST NF-13A.