My 02 quad 5.9 H.O. is overcharging for the third time!! first time was with previous owner,had it fixed by the dealer they put in a new alternator,2 batteries and had the fenders fixed(acid and paint dont mix).After I bought it I put on about 2000 miles and the same thing happened,except for the fenders,I caught it in time. Brought it to the dealer,same thing ,new alt and batts, now its happening again,this time out of warranty, when it does it, if I pull over and come to idle it will return to normal,last night it did it and I hit the cruise button and it went back to normal,(probably a coincidence),If I kill all accesories while driving,it makes no difference,wondering if the grid could be at fault,cause the voltmeter fluctuates like when cold,but then just starts climbing,and this only happens when truck is at operating temp,also when air temp is warm.60+ or cold,30 or below,aslo does not happen all the time,I'm trying to keep track of all parameters when it happens,just hope I can get it before it cooks again, Dealer is clueless,they just want to change everything again.
Any thoughts or suggestions would be greatly appreciated.

 

Alternator charging is controlled by the PCM.

Sounds like they never looked into it.
PCM being a computer can go bad.


phox

 

or possibly a loose or poor ground for the pcm. it uses more than 1 ground.

 

Just tonight I had someone else tell me to check the ground also,so thats my next step,I hope thats it, Thank's for the reply I'll keep you posted.