If the answer to step 518 is yes, the routine continues to step 520 where {HEAD ~ the routine} sets {TAIL ~ the desired exhaust and catalyst temperature} based on the de SOx conditions 
sets
If the answer to step 518 is yes , the routine continues to step 520 where { HEAD ~ the routine } sets { TAIL ~ the desired exhaust and catalyst temperature } based on the de SOx conditions
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH