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; therefore, vehicle must be in closed loop in order for Mode II results to be valid. Closed loop can be attained by operating vehicle at 2000 RPM for about 2 minutes under a no-load condition. In closed loop at 2000 RPM, Red LED will indicate system operating condition as follows: rich - light is off longer than it is on; lean - light is on longer than it is off. Light must change state at least 5 times every 10 seconds. Ideal air/fuel ratio would be 5 or more state changes, 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 simultaneously by Red LED on side of ECU and by CHECK ENGINE light on dash. Light flashes 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 .6-second flashes followed by three .3-second flashes would indicate a Code 33.