I use the FSS interval on my 99. It mainly monitors coolant temp and trip length to determine oil life. Max interval is one year or 16K miles. Mileage can be significantly less pending your personal driving style. It trips for most people between 8-12k from what I've observed reading here.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)