WHAT THE HECK IS THIS?!?!?

On our way to Grande Prairie (GP) from Whtiecourt, this popped up on the dash. The fault is yellow (not red) so we stop at the next roadside turnout (it was only 1 km away) and we called Freightliner to give them the code of SPN 3058 FMI 18 SA0. They advised that this has something to do with the exhaust emissions therefore it would eventually result in the engine being derated (loose power, either 25% or more). The directed us to call the nearest dealership (in GP) for service. We drove to GP and went right to the Western Star Freightliner service centre where they did a quick diagnostic and advised they need to clean a sensor but have no shop time available until Monday. So, plans are changing and very fluid. Before starting this journey, I asked in a Facebook group, what was the 1 thing I should pack or be aware of, and many people said to pack your patiences and expect the unexpected (thank you Big Brother Canada). We have extended our stay in GP until Monday when we take the rig to Western Star at 8:00 AM. Let's hope they can get us back on the road and visiting our Friends Tyson and Han (The Boys) as soon possible as this fault has impacted their Vacation along with ours. Stay posted for more updates!