Mode II (Exhaust Gas Monitor)

In Mode II (engine running), both red LED and CHECK ENGINE light are used to monitor air/fuel mixture feedback control. Vehicle must be in closed loop for Mode II results to be valid.

In open loop, red LED remains either on or off. In closed loop, red LED indicates if system is running rich (light off), lean (light on) or at ideal air/fuel ratio (blinking synchronized with CHECK ENGINE light).

If 2 oxygen sensors are used (left and right side), left side is monitored first. To switch to right side: With engine running, turn screwdriver fully clockwise. Wait at least 2 seconds. Turn screwdriver fully counterclockwise. Inspection light will begin to flash. This is Mode II.