ISHODU,
The computer "codes" when it does not get the signal from a sensor that it is programmed to expect. A "code" from a specific list of sensors will activate the "Check Engine" light.
The HEGO, or more commonly the 0-2 (oxygen) sensors "switch" from rich to lean continuously as the exaust gas flows by them.
If a code is set because the 0-2 sensors stop switching, and stay in either the lean or rich condition, the computer codes (and activates the CE light).
The question is, why did the 0-2 sensors stop switching? Are they in fact reading a rich condition? Is there a poor connection, an open or shorted wire interferring with the "signal"?
Or, do you have failed sensors?
I put the failed sensor question last to make a point. The point is that a "code" does not automatically mean a failed sensor. It is wise and economical to check out the other possible causes of the "code" before replacing a sensor.
In the instance you describe it would seem that you had an intermittant rich condition that resolved itself. If it returns and stays, then start looking for the cause.
Cold Molsons for everyone! cheers rangerj
