A weak battery may result in illumination of the Check Engine Light with fault code P0603 stored.Google+
Car Problem Reports
Infiniti G37 Check Engine Light With Code P0603
Infiniti G37 Problem
Average Mileage: 17,950 mi (5,900 mi - 30,000 mi)
Visitor, 2009 Infiniti G37, 5,900 mi
Brought my car used and it had a auto starter that i didn't know about so one day i used it and the car did not crank on all the way which caused the engine light to come talking about service vehicle soon (What!!!!!). Then when i tried to normally start the car i could hear a hesitate so i knew it was a battery. Got that changed but the light was still on. Looked in manual and it said the gas gap could be loose after like 30 starts the light went off. I could have went to the dealership but i knew nothing was wrong with the car just don't panic if it happens to you. Give it two weeks if the light doesn't go away then take it to a mechanic
Dealer replaced defective battery - prorated cost paid by buyer.