Welcome to the forum...
I don't know the answer to your question, but I believe sometime ago I read they were on the sides of the converter; nearly impossible to see or change without pulling the converter. Hopefully you'll hear from someone that actually KNOWS the answer.
You might try the 'search' function for this site and see what you find.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.