2004 pontiac grand prix, check tire pressure, charging system failure, check engine soon warnings on DIC all come on and has been on for a while like 2 months. I have been to both autozones in my town and penzoil and walmart and all of them cant get a code from the car. Every so often "reduced engine power" comes on and you cant accelerate anymore and very hard to turn. Have to pull over and shut off and open door then start it back up to b able to use car properly but yet again the other 3 warnings come back on the DIC. Advanced auto checked the battery and the altenator and both are good. Everyone is stumped as to what the culprit is so pllleeeaassssee help thank you
