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Kyle Gandy

After treatment catalyst

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What causes a SCR catalyst to go bad. I'm guessing over dozing of def fluid, or soot buildup. is there a way to clean one like they can bake the DPF filters?? had two in the fleet go out now. Ran SCR system text and every thing check out good, fluid dozing measures to spec. I replaced dozer to be sure it didn't hang open at times maybe.

Edited by Kyle Gandy
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Well hell, idk the dealer said they have seen only on bad. I hade one throwing a dozer code every thing was workin fine food def quality, all test checked out good. Replaced dozer did several regens and rest drives long ones code would clear then come back right after putting back into service. We had a new wrecked truck out back with only 1000 miles. Put that catalyst on the truck ran one regen and no problems sense. And now there is another on that seams to be bad.

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If there are no problems with the engine releasing too much NOX, like some sort of EGR system issue. Try replacing both NOX sensors and make sure the ECM & ACM software is up to date and perform a regen. If the fault can be cleared after the regen the problem is most likely fixed, but 4094 faults can be a pain to repair.

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Never heard of the SCR " mixing box" go bad. Are you doing the crystal sublimation regens? They are different type or regen that dont dose DEF and get hotter. There is a Mack service bulletin that has some tips on the 4094 code. It's SNM 13-022 if u have acess to the Trucks dealer portal through Mack. I cant seem to attach the bulletin or even make a copy of it for some reason. If the DEF doser seems to be working correctly, replaced both NOx sensors as said above.

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The newest NOx senor part numbers are 21636091 for the pre-SCR (bottom of the DPF) and 22014032 for the post -SCR (SCR box outlet) . Working on a truck now that came in with SCR derated 5MPH. Active codes SPN-4094 FMI-18 and SPN-5394 FMI-17. Did all the DEF doser test and all good. replaced both NOX sensor with newest sensor, updated software in engine and SCR ECM's and did crystal sub regen and a regular regen, all OK. I do about 1 a week of these.

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Awesome. Getting the sensors now. Haven't had a chance to get back to that truck yet. A lot of brake downs lately. I will def. do that I have try the crystal sublimation regen with no luck. Thanks for all the help.

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Doing another NOX sensor replacement this morning. Super nice 2012 Rawhide has Active code of SPN-5394 FMI-17. Truck has been to 4 dealers in the last 4 weeks and nobody changed the NOX sensors. I hope this fixes it! LOL

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I have to put the catalyst back on. These guys knocked the ceramic filter out of the one I replaced in another truck (ig try into get more flow idk how they thought it would fix it) I'm no pro but I've learned a lot and I know they don't put something on the truck you don't need lol. but hopefully it works. Let m know how yours goes.

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I've done several crystal sublimation an regular with no luck. I don't have access to the portal how can I get registered. Dose the company have to pay for it?

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Your local dealer has to apply for you ( I think) . Its called "Trucks Customer Portal". We have never set it up for any one yet.

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Ok. And what exactly is it. So I can get my boss on to it if we have to pay for it. All the service info I'm guessing ?

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Good news. Sometimes the codes wont go inactive after replacing the NOX sensors , we have to clear the codes and test drive or do acouple of regular regens.

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Ok I have a quick question i have checked everything above and all comes out fine the Egr cooler looked plugged and it has been replaced so has the veturi tube. my question is i have a truck throwing the 4094 code fmi 18 when you are doing a regen on it, the temps do not come up constantly but it will disable regen the dpf intake temp will come to 1050 and outlet will sit at 700 then outlet will come up to 1050 and inlet will drop to 700 both time regen stops and starts. I do not have any issues from filter already dropped out and checked cleaned everything tests out perfect still have 4094 and will have trouble starting when truck is sitting for about and hour or so 

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I am new to this forum, I am a independent shop that works on a fleet of Macks. Was there any response or answers to Rookie's post on oct. 25, 2016

 

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