2005 Chevy Equinox ECM and check engine lite issues

So now my mechanic is telling me that there is a short in the ECM of my 2005 Equinox that is causing the Check Engine light to come on. He has cleaned out all the carbon and replaces the EGR valve. He tells me that I will have to take it to a Chevy dealership and it will cost around $655.00 to replace and program. I just want to sell this car, but I can’t until I get it running right. I refuse to sell my problems to someone else. I have already sunk about 2+ grand of recent repairs into this car, so I am hoping someone will have a suggestion on a cheaper way to fix this issue. He tells me that the when that when a EGR valve was put in a year ago someone (another mechanic) crossed the wires which has led to the short.

Thanks as always for your responses.

Fairfax

Specifically, What DTC(s) (Diagnostic Trouble Codes) Are Setting The CEL (Check Engine Light) ?
Please List Any And All Codes.

Without knowing this and the competency level of your mechanic, most of us know less than you, mechanic 2, and mechanic 1, put together.

Cars are sometimes difficult to diagnose and repair, but try it with inadequate information and no vehicle in front of you.

CSA

Has DTCs P0601, P0602, P0603, P0604, Or P1621 Been Found ? If So, Has The Vehicle Been Checked For A Possible Low Voltage Condition That Could Possibly Set One Of These Codes ?

Besides a CEL, what other symptoms, if any, does this vehicle exhibit when driven ? What caused mechanic 2 to work on the EGR system ?

CSA