2008 Envoy Denali 5.3L - Need to identify this part

Hello All,
I was hoping that someone could help me with what part needs to go into this location. It looks like some type of sensor hole or plug. I can't attach the picture so I added a link to the engine that I found on ebay. The hole is the one that has the red cap in the picture down by where the starter motor mounts (Lower left). It looks like it is near some type of sensor. Any help would be very appreciated. Thanks!

http://www.ebay.com/itm/Trailbazer-Envoy-Z71-VIn-3-M-Engine-2007-2009-5-3L-68K-MILES/112548146227?fits=Make%3AGMC%7CModel%3AEnvoy&hash=item1a34646c33%3Ag%3AgoAAAOSwXetZXSxX

Welcome to AF, what is in that hole in your engine? Not sure but it should be the crank senor.

that hole is for the dipstick, the crank sensor is further back.