Low Power Insicator on 2004 Chevrolet Silverado 2500 HD

Low power and engine light on. Truck's on low power, I left the truck running for 10 or more minutes, turned it off and on and finally it ran normal. The engine light stayed on. This has been going on for sometime. Mechanic could not find any problem?.? Does low battery have anything to do with this problem? Any suggestions will be greatly appreciated.

Asked by for the 2004 Chevrolet Silverado 2500 HD
Have it scanned and post the codes so we can advise..