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P0603 is normal, for a tuned truck. I assume you have some sort of tuner on it? It is because the stock tune is removed and an aftermarket one is there now, the PCM doesn't recognize.
Thanks for the quick reply Strokin7.3 yiup tuner cool. The weird thing is I am not equipped with dual alternators, so I guess I won't worry about those huh? Thanx again sir.
Try unhooking both batteries, turn your headlights on for about 20 minutes. That should reset the codes. P0603 will keep coming back most likely, but i dont know what is up with the dual alternator codes.
Reset codes then Charge your battery completely with a charger.
Turn on lights for 5-7 min to take off the surface charge and test batt voltage. Should be at least 12.5V
then test the alt the old fashioned way....
Start engine and voltage should be more than what battery tested at but not more than 14.5V.
then idle at 2000rpm and turn accessories on incl. fan blower and head lights. Shouldn't drop below what battery tested at. The stock alts are real weak anyways and the auto parts store checks are usually worthless.
They'll show alt good when its toast most of the time.
A good Voltmeter won't lie.