Originally Posted by mtnmerlin
The procedure to reset the SCR system by driving 60 miles at 50-60mph may be golden words. I did that today after clearing the code and the MIL is now off after stopping and starting. However, the Torque App still shows the P20EE code as active. At least the MIL is off.
BTW, I saw it do two regen's while the MIL was on with the P20EE.
I'm afraid you are simply experiencing the normal cycle for setting the CEL from a pending code. The CEL comes back after a certain number of drive cycles and/or miles *IF* the onboard emissions testing is still failing. My experience has been that the P20EE code occurs because the SCR system (DEF system and Catilytic Converter) is operating below efficiency. Mine would take 130 to 170 miles to turn the CEL on after a reset.
I've been saying there is a problem with the Catilytic Converter for a while now. Either the cat converter is defective, the system design is flawed, or there is something physically damaging them. Unlike gas engine cats, ours is not mounted upstream in a protected location near the engine but is located low between the rear wheels. It operates at 500-650°F but spikes to 1200°F due to the upstream DPF temps during regen. Thermal stress and mechanical impact are the top killers. If you tap the converter and hear rattling, it's internally damaged. Impact from road debris can cause this. Also quickly quenching the high temperature with water can crack the ceramic honeycomb catalyst.
With its low location, I would not recommend driving into deep water or spraying water directly into the pipes when washing especially right after a regen. The dual tailpipes angle down a short run of pipe to the cat.
Those are just my suggestions for precautions until we know exactly why the cat is failing so frequently.
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