On my ZX-10, I heard that you get a check engine light when you unplug the switch for the PAIR valve after you start it up instead of before. The charcoal canister isn't plugged into anything electrical though so it wouldn't throw a code unless there is a huge vacuum leak from ports not being plugged I guess. Other than that, he probably just left something else unplugged.
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02 RC51
04 ZX-10R
09 Speed Triple
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