This is the green plastic "U" shaped pin-retainer clip that slides into the ECM connectors on the 2004.5-2005 LLY Duramax. It is very common to either lose or break this small clip 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...