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DEF only works in the DOC (catalytic converter). The urea in DEF breaks down to ammonia when it hits the hot exhaust stream. The Ammonia reacts with NOX to form Nitrogen and water in the DOC. It would have little to no effect if injected downstream of the DPF where there is no catalyst to aid the reaction. As far as I know, DEF is only injected upstream of the DOC. The rate of injection is determined by NOX sensors downstream of the DOC.
 

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My 2011 had a filter cleaning message, my 2019 does not. I contacted the dealer and they confirmed there is no longer a message displayed.

You can smell burning scent when the truck is in regen and you step outside the truck.
 

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DEF only works in the DOC (catalytic converter). The urea in DEF breaks down to ammonia when it hits the hot exhaust stream. The Ammonia reacts with NOX to form Nitrogen and water in the DOC. It would have little to no effect if injected downstream of the DPF where there is no catalyst to aid the reaction. As far as I know, DEF is only injected upstream of the DOC. The rate of injection is determined by NOX sensors downstream of the DOC.

Oops! I see I put the DEF in the wrong catalyst above. The DEF works in the SCR, not the DOC. :eek:
 

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As mentioned DEF is used to reduce NOx.
NOx is produced at high combustion temps. ( Think when the Turbo is in use)

If you have an Edge CTS or other gauge you can see your EGT temps at the 1st probe. High temps mean you are probably using DEF. Low temps you are not.

So when your truck idles at 750 rpm it is showing 300° EGTs. Running at 65 mph on level ground will show 1500 rpm and maybe 500° EGT. Accelerating up the onramp might see 20 psi boost on turbo and 1000° EGT. And towing 13,000 lbs at 70 mph will more like 800-900°, And trying to hold that 70 mph up a 7% grade will read more like 1100°

I don't know what the kick in temp is where DEF starts to inject. But it's safe to say at idle you are not using any and at full throttle you are.

Your emissions in the exhaust pipe are really two separate parts. DPF to clean soot and SCR to remove NOx.

On another note, Your Passive Regens will happen anytime your EGTs exceed 572°. So if you get over 572° and are not producing excess Soot, Your passive regen will burn off the soot in your DPF.
 

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I can tell when it’s in regen. It will sound like the fan is engaged and your truck feel like exhaust brake is on. It’s a bit more jerky. Or open your windows and you will smell a burning smell. But never seen a message for it. Filled up def 3 times now. Only at the big truck stop no issue except pump keeps kicking off every couple of seconds and not even being full yet. It uduallynaround 2.79 a gallon for def and the diesel pumps does not shut off at the 100 dollar limit.
 
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