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P20EE00 SCR catalyst efficiency below threshold


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Hey guys I am just wondering if you guys have any Self made Diagnostics that you use like a check lit for the dreaded P20EE00 code I have replaced two SCR'S via E-service under warranty I have had this code a few times on trucks that are not under warranty and I have replaced the dosing valves the flex pipe between SCR and DPF and  NOx sensor very once in a wile and to a Sublimation regen, but I feel I need a better check list then what CBR provides Thanks for the help in advance.

ps were a small dealership and not very many guys here that have several years of experience

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P20EE general causes, Exhaust Leaks, Fuel contamination, Faulty Diesel Particulate Filter (DPF),Faulty NOx Sensor,  contaminated DEF or Faulty SCR Catalyst.

Since you have done most of that at one time or another, I would start by visually inspecting the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

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I think in the last CBR bulletin I saw, it wanted you to look at the past history of the truck , like a failed turbo or EGR cooler . Where oil or coolant could have made it to the DPF or SCR box. This could “ poison” the SCR box. Software updates help sometimes . We have been lucky and have not had to replace any SCR boxes on our 30 CXU/Anthems yet . We did have a cracked DPF filter causing a P20EE  code once , see if the exhaust stack black or clean 

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( Faulty SCR Catalyst.)  this is a possibility Its been quite spotty and we have replaced several ! How ever you got the follow the the rules of engagement Or warranty won't pay if you have any left! 

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so I have been finding exhaust flex pipes that have been broken near NOx sensors and that has been causing them to read incorrectly. also there has been a lot of crystallizations build up on the flex pipe between the DPF and the SCR I have found two lower DPF housings that are cracked next to the Def injectors (it is a hair line crack) (also have been told that it can crack on the flange for the Exhaust flex but have to heat them up to see cracks) but that cause fresh air to get in to the dpf and scr and causes crystallization build up witch interrupts the exhaust flow and causes the P20EE code hope this helps others.

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