Run the 90 degree spacer on the post o2 sensor only - the pre-cat o2 sensor should be installed right into the bung on the header.

This way the ECU sees the "difference" between the o2 sensors, there is a cleaner reading at the rear, the CEL should go away after a few drive cycles once you do that.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards