Mode II

If engine is started with ECU in Mode II, Red LED is used to monitor air/fuel mixture feedback control. In open loop, Red LED will remain on or off so vehicle must be in closed loop in order for Mode II results to be valid. Closed loop can be attained by running vehicle at 2000 RPM for about 2 minutes under a no load condition. In closed loop at 2000 RPM, Red LED will indicate if system is running rich (light off longer than it is on) or lean (light on more than it is off). Light must change state at least 5 times every 10 seconds. Ideal air/fuel ratio would be 5 or more changes of state with equal on and off time indicated by LED or CHECK ENGINE light.

When Mode II is accessed and engine is not started, codes stored in ECU memory will be flashed by the Red LED on the side of the ECU and simultaneously by the CHECK ENGINE light on the dash. Flashes of the light will consist of long and short duration flashes with approximately a one second pause between flashes. A 2 second pause will exist between multiple stored codes. For example: three 0.6 second flashes, followed by three 0.3 second flashes would indicate a code 33.