2011 Peterbilt roll off SCR

Replace the outlet NOX sensor

Datalog or monitor and road test operating steady state on the highway with cruise set.

Looking for SCR eff. to reach high 90's to 100%. Outlet Nox ppm should be single digits to near 0

The outlet NOX is your key player on the DEF dosing rate and SCR eff numbers. It is most likely Biased high.

Frequent regens.......

I would like to see you regen History. Regens should be 25 hrs. If sooner suspect Biased or stuck in range DPF pressure sensor. Check freeze frame data for all stored codes, DPF pressure may show 900 plus PSI. Dead giveaway bad sensor. Check pressure tubes for blockage and proper orientation.

Consider Engine managment cleaning as well, Boost sensor plugged?

 

Remove the sensor from the pipe start a regen to increse exhaust temps and monitor the sensor once it comes online. Out of the pipe it should also read near 0 ppm.

Have you flow checked the DEF doser and measured its flow/volume rate to be in range? Decomp pipe is clean and diffuser grid in place?

If the Nox sensors and DEF dosing is accurate. The only thing left is SCR itself. Dont replace many. Inspect SCR inlet for blocked cells or face plugging.