Reoccurring DEF problem - Freightliner 2013 DD15

Replace nox inlet sensor. Replace one box. Or...let nox outlet sensor hang free like someone above suggested.

 

correct !

 

how about nox inlet value ? 200-300 ppm?

 

I just ran into this. As long as your truck is a GHG-14 (Has the electric DEF injector). And while watching your SCR conversion % during a parked Regen you start with good conversion rate, then watch if fall in painful disappointment.

Any way, They make an awning kit to aid in the SCR conversions by deflecting the exhaust around the Injector to mix the DEF with the exhaust better. We also blew out the DPF’s and the DOC’s with shop air while we had the DPF’s out to install the awning kit.

I’m hoping this process will work on the other 3 sister trucks that are having intermittent SCR Conversation Low codes.

 

Guys please help.. Higher PPM on outlet than inlet

 

I’ve run into this before, it’s overdosing DEF or your SCR is corrupted.

After some research, the SCR conversion is really delicate. To much def or not enough working catalyst (SCR) will actually create NOX.

I wasn’t impressed either......

 

I did def quantity test ..120ml

 

I’ve got 3 trucks that where/ are doing this same thing, the oldest unit I think we messed up. We tried and Idea where we thought the SCR was sooted and needed cleaned. We injected straight water directly into the SCR during a Regen. To our surprise the NOX conversation was perfect through the rest of the regen and part of the next. The next day we ran another regen. The nox conversion inverted after about 800 deg. And we never could get it to pass conversion again. We are currently trying a more time consuming approach mentioned here.

The two newer units have the GHG 14 emissions. After we replaced both NOX sensor without any correction. We Attacked anything that did not quite look right. First unit we replaced the doser valve, doser injector, replaced the DPF’s (50%early), blew out doc, installed DEF awning kit. And one-box wire harness. It was fixed for about a month. And the codes returned. Not inverting like it was but still throwing lights. Monday the during the regen we noticed the requested and actual DEF injected where from 200 to 600g apart.

The next parts cannon will be loaded with a new DEF injector and pump. It’ll get installed Monday.

But because all this I’ve start looking at the chemistry of the SCR system. I found out that the Ammonia (Urea) in DEF can just as easily make NOX as conver them to Nitrogen, oxygen, Carbon dioxide and water. It’s a delicate system the’ve Added to millions of the heavy duty diesels in American.

 

before to touch any part of emission the value of inlet NOx sensor must be monitored. Sometime the problem is the engine and not emission system.. Under full load(on dyno machine) engine's exhaust gases must contain ~ 550 ppm nox. If value is higher then nox sensor is bad or engine has worn parts(most likely valves and rings). I have seen many worn engines blowing alot nox. One box has limit of conversion and in some point it will throw low nox conversion code.

 

Dosing wayy more DEF then requested ?