Have you ever removed the DEF injector right in front of the SCR? The injector gets all plugged up with crystalized DEF.
I clean mine everytime I change the oil, sometimes sooner.
Best way I've learned to tell now if it's plugged up is if I take a quick wiff of the exhaust, if you don't smell def, it's probably plugged or only 1 of the three injector ports is getting fluid through.
It's super easy to do and only takes 2-5 min. (maybe a little longer the first time, it's one allan key to remove the clamp, then hit it with steam, and put it back in)
You'd be surprised how badly crystalized the injector gets even with 3-4 months, it's all crystalized and plugged up right there. If you've never cleaned it, I bet the problem is a plugged injector, and of course the dealer wants to sell you more stuff...
It's so easy to remove, there's a great youtube video, and if you have a hand-held steamer, that works perfect as that will liquify the crystals and the injector comes out spanking clean...
Here's the video from Shawn, who's sadly no longer with us... but has done a lot on his 2014 to help the rest of us.
Scroll ahead to about 4:25 when he experiments with a steamer and realizes DEF chunky crystals comes off like butter leaving the injector brand new again.
