Hot exhaust/Exhaust filter full LIGHT

Hello drivers, I'm a student driver O/O
I own a Freightliner Columbia Detroit engine.
It's an 2008 a mint condition and has 500k miles.
The Hot exhaust/Exhaust filter full LIGHT appears on my dash board, I looked in the manually and it states that a qualified mechanic should look into it, I'm not a mechanic, I know my pre-trip that's about it. I asked a couple of drivers that has the same tractor they said not too worry about it. When that light appears press ad hold the button for 4 seconds and it'll go away. It comes on once in a while, this time it came on and didn't go away and started flashing I pressed and held button down, and nothing happened. Then I pulled over, turned the engine off waited a good 10 mins, restarted it and continued driving , and the light was on but wasn't flashing then it went away...is there some kind of filter for the exhaust, it's dirty maybe? Or it's just that this is a Detroit engine and those engines are very hot I heard ,so that's why the light appears? Plus I noticed my upper muffler pipe on top where some trucks has a rain cap, it's rusted on top there and you can see that the rust trail worked its way down on the outside of it .. I don't want to damage to my truck. Please drivers if you have some knowledge on this please help me I appreciate it. These are the pictures signs/warnings and tr button.. See the manual I have it's not the correct manual for this truck I'm sure of it, the pics don't match exactly what I have onto tractor.

 

this is the light that's it's showing
And then it flashed on me continuously yesturday for the first time. " exhaust filter full" and it tells you the steps on the picture push button 4 seconds etc...

 

Is this the filter you guys are talking about?

 

Wether it flashes or just appears, you must be parked and press the button correct?