my 'check lite' comes on intermet. every time I look "my engine is still there ?

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my engine lite comes on and stays on for a few daze the off again. very intemittant. can not get a code reading when it not on..Ifigure EGR. is that the device on the top of the engine that has an 'adjustment valve' on it ??? appreciate the help.. the service manuals I have are only the "block diagram" ones...thanks in advance. 143.000 miles and runs like a 'bdd''