It's a sensor. . But not fluid. . The lines are there but separate part of the system and not connected to the sensor

Wups my bad... not lines (they different section and lower down.... I forgot where I just took a photo? Lmao) .. the corroded bit is the mounting bracket/rail that the sensor is on... and the corrosion itself is just result of bad galvanizing

Do you really mean not for fluids, as in no liquid or gas, including air?
If so, then that pretty much leaves temperature, atmospheric pressure, vibration, and radiation (all types).
That part in the lower left is IP67 rated, so it's water and dust proof, to a degree.
I'm drawing a bit of a blank. Any of my musings jogging any brain cells free guys?

It definitively has no oil, gas, liquid of any kind. . 

Its on a truck at my work. . There are about 12 of them in total (some different shape but all same function) 

They are very important on all the trucks I work on!

LPW .. Feb 24

Probably a gas (non liquid) sensor then... Co2 or something?

He said not any sort of gas...
GPS maybe? Can't imagine why that would be under the truck though.

@Janx: What's LPW ,, Feb 24 mean?

Whoops, thought he meant fuel 

He may have, lots of people call all types of fuel "gas". However, I think Janx is in the UK, so I assume he'd call gasoline petrol.
Am I even close, Janx? Lol

Light sensor

I'm Aussie!... lol. .. not GPS, NOT liquid of any kind .. not fuel/gas/petrol/gogo juice..  Suresh and stone the crows!

Not light. ..

On the side/rear of truck. ..

You guys don't know LPW? Omg!

Tard farm, last post wins.... thread!... find the date..  mention my work place! ... not doing ALL the work for ya! Fair dinkum mate!

Suresh?.  Sheesh!

backup sensor or is it a rear camera?

Blind spot sensor?

Mmmm nope!.. good thinking tho! ... it is a safety thing. . Just not the ones you guys mentioned. .. work further thru the possibilities! . 

And you've really got to look at everything in the photo. .not just the sensor!

Some gyroscopic thingamabob to measure tip angle? I've got no idea. Temperature?

Not temperature ... Not gyroscopic... But ..Tip Angles.... That's vaguely along the right path...

These things come into play when we go to unload the trucks ...

Guys

Maybe look up some vids of modern waste trucks .... Unloading....

Once you see the process .. It might bring to mind what such a sensor would be used for 

Proximity sensor for sensing when the rear gate is fully closed?
Or is it to sense when the truck is empty and the garbage has stopped coming out?

Proximity it is! ... Little magnetic job .. When the steel whatever moves away an alarm goes off in cab.

They are all over the load area of truck.... Scoop blade, hydraulic ram travel, inspection hatches etc

You got something this go mojo?