This is the black plastic wire-dress cover that snaps onto the ECM connectors on the 2004.5-2005 LLY Duramax. It is very common to either lose or break this cover when disassembling the ECM connectors to install an EFILive DSP-5 switch or high-idle kit. BT DieselWorks has you covered with a genuine Delphi-OEM replacement part. This clip is NOT serviced separately from GM; if you go to the dealer, they will only sell you an entire replacement connector. Why pay the dealer $75+ for the entire connector when all you need is the plastic cover?
Select which ECM connector you need the cover for. C1 is the small top BLUE connector, C2 is the large middle BLACK connector, C3 is the small bottom GRAY connector.