SCR Diagnostics with Tailpipe Analysis

[JoeR]

Last spring a member here, Bill Bledsoe, started this thread :  

 

Bill and I got talking and I wondered if using tailpipe analysis could help with SCR Diagnostics.  I've been playing with it for the last year.  It works.  The problem it solves is that the NOx sensors in the truck can't tell the difference between NOx and Ammonia (NH3).  So when the catalyst starts to fail, both unreacted NOx and unreacted NH3 go out the back.  The rear NOx sensor sees it and counts it as NOx.  A partially failed SCR can look exactly like no DEF injection to the NOx sensors on the truck.  Please take a look at the youtube video I have explaining how it works.  Let me know if  it is good at explaining the process.  I'll post some actual case studies next.  This info is not dependent on any brand of equipment.  I'm showing Snap-on stuff because that's that I have.

Thanks,

Joe