The exhaust control system includes an exhaust control valve, and {HEAD ~ a primary and a secondary exhaust purifying system} located downstream of {TAIL ~ the exhaust control valve} 
located downstream of
The exhaust control system includes an exhaust control valve , and { HEAD ~ a primary and a secondary exhaust purifying system } located downstream of { TAIL ~ the exhaust control valve }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL