Such a condition may be requested by the routine based on {HEAD ~ an evaluation} of {TAIL ~ emission control device performance}, and based on a fixed number or time of engine and vehicle operation 
of
Such a condition may be requested by the routine based on { HEAD ~ an evaluation } of { TAIL ~ emission control device performance } , and based on a fixed number or time of engine and vehicle operation
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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH