i recently dropped an 03 engine in my 01. one thing i noticed and cant find any info on it on the driverside on the engine block just behind the motor mount it looks like there is a plugof some sort mounted in the plug. its cresent moon shape with 3 prongs inside. any one have a clue? the 01 didnt have it anywhere.

 

if its in the freeze plug its a block heater

 

ya it is in place of one of the plugs.