Article Link

An excerpt: "In one instance, cam timing on an older Honda will cause an oxygen sensor failure trouble code to be stored in the engine computer. In essence, higher than usual intake manifold vacuum tricks the ECM into excessively leaning out the air/fuel mixture ratio. Because the air/fuel ratio is so lean, the oxygen sensor fails to switch, which leads the ECM to "believe" that the oxygen sensor has failed when, in fact, the sensor is in perfect condition.

Its just an article dealing with timing belt installation and possible effects of installing it one tooth off. It was an interesting read for me as it shed light on possible reasons why the CEL may come on.

EDIT: Here is the LINK to the main home page that has several other online magazines that deal with auto diagnostics and such.