When the service indicator light comes on, I recommend bringing your vehicle in to a reputable service provider to have your engine scanned.  If the results disclose a spark plug error, it may be due to the fuel injector and throttle needing to be cleaned.  I was getting the spark plug error after having all the spark plugs replaced within 16000 miles which is less miles than should have caused this error.  Then 2 months later, the service indicator light came on.  When the engine was scanned, again, the results disclosed the same spark plug error.  This time the spark plug was replaced and the fuel injector and throttle cleaned.  The auto maintenance shop recommends this type of cleaning every 30,000 miles.