Wire harness can cause all kinds of codes b/c there are shorts in the wiring..

If the harness is bad , it has to be replaced before anything ese can be determined, regarless of which modules you go into for diagnostic codes.

But an EGR code is usually a mechanical blockage problem on that 104 engine and my post explains how to determine/test if that is , in fact, the problem...regardless of wire harness/

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A Dalton