2019 Cascadia 126, DD15 at 475, DT12, 612,000 miles. dry van, leased on, home to Knoxville on weekends.
this truck used to go a whole week without me noticing a regen. for the last month the high exhaust temp light is on every 300 miles or so, and fuel went from 7.1 to 6.6 over the same lanes. no check engine light, no codes on the dash. it pulls fine.
i know the dealer will want to plug in and charge me two hours to tell me something. before that, what did yours end up being?
start cheap. on that truck the DPF differential pressure sensor reads through two small hoses. if one is cracked, collapsed or full of soot, the ECM thinks the filter is loaded and kicks off regens it does not need. look at them with a flashlight first.
if the hoses are good, my next suspect on a DD15 doing that is the hydrocarbon doser, the one people call the 7th injector. it sprays fuel ahead of the DOC to heat things up for the regen. when the tip cokes up it sprays poorly, the regen does not finish, and the truck tries again a few hundred miles later. that would match your fuel drop too.
how much do you idle? and Detroit's maintenance schedules and the aftertreatment intervals are on demanddetroit.com if you want to see when the DPF was due.
had the same thing on an X15 two years ago. it was the sensor hose, cracked right at the clamp where you could not see it without pulling it off. 9 dollars and fifteen minutes. check that before you spend money on anything else.
hoses are fine, both of them, i pulled them and blew through them.
broke down and paid for the plug-in. the tech found a stored code that never lit anything on the dash. 3556, which he said is the doser quantity being off. idle percentage on the report was 19, which seems high to me. so marcus called it.
that is the doser. you can try having the tip cleaned but at 612k i would just replace it, the part is a few hundred dollars.
and while it is apart, have them look at the face of the DOC. if the doser has been spraying wet for a while, the front face of the DOC glazes over and the next regen will not work right either. a new doser on top of a plugged DOC is a common second visit. 19 percent idle does not help, that is a lot of cold soot.
same story on mine last fall. the shop said the root of it was my idle time, mine was over 30 before i fixed my battery setup. clean out the aftertreatment and keep idling and you get to pay them again in a year.
done. doser replaced, 512 for the part. the DOC face was plugged like marcus said, so the DPF and DOC both went out for cleaning, 690. with labor the whole bill was 1,980.
three weeks and about 6,000 miles since. back to regens i do not notice, and mpg is 7.0 on the same Chattanooga to Dallas lanes. i bought a cheap battery cooler setup off a buddy to get the idle down. still learning to sleep with it.
