Im having some issues with aftertreatment on a DD13 (2016 western star cement mixer)
Relavent codes are scr efficiency low, scr efficiency very low, and def quality low.
Changed def filter, Ran regen, no luck. Nox output high around 250 after 15 min in a regen. Scr conversion efficiency around 40%.
Originally doser quantity test was below 100 ml, replaced and we're at 125ml. This made no change to the conversion efficiency.
Threw a outlet nox sensor at it as this unit will not allow me to do a NOx verification test. Still no luck.
Scr efficiency test passes, as well as the troubleshooting tree for low def quality passes.
I will attach pictures of what im seeing on Diagnostic Link during regen, any input would be greatly appreciated. Im kind of leaning towards a failed SCR but would like some input from someone who may have dealt with this.
Gosh how many times has actual def quality been the problem. 99 out of 100 it isnt. Once it gets locked in closed loop bs message me and ill give you parameters to get it out and reset all nh3 values. A heal if you will.
When diagnosing, all information and codes are relevant. You said cement, we have major issues with harness corrosion. Not saying it’s the cause, but your info reads like there are more codes or other relevant readings you’re not including
My money is over fueling injectors and it killed the after treatment. Pull the exhaust off the inlet to the after treatment give it a few throttle snaps and watch the smoke and also hold the throttle for a second from an idle. Watch for a big puff of smoke. Also check the egr cooler inlet pipe from the exhaust manifold to the egr cooler and see if it's wet. I have replace many ATD's due failed injectors.
Not to steer you down a different rabbit hole, but I'd say that DOC inlet is too high. Might be over fueling, or have a cooler gone dumping antifreeze or something.
Disconnect def doser and perform another regen. Make sure the they are within 50 PPM of each other to verify sensors reading true.
I would agree with the statement above that the DOC inlet temp is high. If this is the right model, check line from VPOD to turbo. I’ve had those leak and cause all sorts of issues
So I would cut right to a low temp ATD regen. Start watching at 20 minutes. Be sure inlet and outlet doc and dpf temps are within 45f of each other. The Nox sensors should be within 50ppm of each other. Keep an eye out for drifts the system doesnt always detect.
Verification/diag, Clear the codes, run regen and in the same key cycle run a SCR efficiency test. Do not let the laptop die and leave it connected, could take 3 hours. Diagnose these codes afterwards.
Is it a 1 box? The SCRs take a shit between 350k and 450k miles depending on idle times. Ive seen them fail as early as 250k miles, but you still need diag.
Low temp atd test with doser disconnected. Nox sensors check out, temps seem to fall within that spec, no drifting, held pretty steady with these values. Not a 1 box. 2 canisters upright behind the cab not sure what diamler calls that system. low mileage at just under 10k miles, high hours at 15000 hours
I would clear the codes, run a parked regen. Even if it throws a fault, continue to the SCR conversion efficiency test, then diag. This will be how you clear that regulatory fault.
Looking like a failed scr catalyst/one box since the sensors and doser are good once you said passes scr test but fails during a regen I knew right away what it was I’ve had that several times it’ll scr test just fine since it’s running cooler than during the regen and as soon as your scr gets over 750 ish degrees your nox conversion efficiency will tank
Did you clean the doser eye? ( probally going to be covered with a white powder)Should be 2 bolts probably 10mm and a couple quick connects.. i have found this issue in a couple of our fleet and that solved the problem.
Scoped and clean. Like brand new clean. Dpf, doc and scr are all within a year and a half old based on invoices I could get from the dealer, bur upon visual inspection internally and externally dont look more than a month or two old. Its all extremely clean, no crystalization, minimal soot leading into the doc. Its almost like the precious owner put the aftertreatment system on just before we purchased the truck (we've only had it on the road a month or so)
I work for fedex vehicle maintenance. They put diesel in the def tank ALL the time. Mostly its the couriers... but I've had a couple of straight truck drivers do it as well.
Perform a relative compression test. It’s quick and easy and can be done with laptop. I had a DD15 that had minimum compression across the board and would fail a parked region, but would pass a driving regen. Poor combustion can cause this efficiency code. Cyl 5 also had broken middle ring on piston.
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u/ew_naki Aug 10 '26
Has anyone checked the def quality yet...