Alternator issue

Justin Bradford

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I am having issues and and stuck in what is wrong. My car had a p0626 code so I first went to replace the alternator. Now with the new one in it’s has the same issue of dying when idling and now has a code p0620.
 

86GT351

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What year is your car? Have you verified all the fuses are good? There are 2 fuse panels. The underhood panel which is the Battery Junction Box and the Smart Junction Box which is behind the passenger side kick panel.
 

Justin Bradford

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It was an ultima and I did not confirm that it was needed I just assumed since the battery was not holding any power and all of the electronics began to fail. I did check the fuses in the hood and found nothing blown but haven’t done so for the interior
 

DieHarder

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Your issue might be ground related. Recharge the battery to full potential and run some tests.
1) What's the running voltage across the battery terminals at idle? If below 14.5 vdc test for voltage drops.
2) If you have a VOM (Volt/Ohm Meter) test for voltage drops from the passenger strut tower ground to the case of the alternator. If you read any voltage (even a volt) your grounds need attention.
3) Also do a couple of voltage drop tests from the alternator body to parts of the engine. If you see voltage indicated on the VOM same issue. This is an example of floating grounds (i.e. Ground reference is at a different potential/floats compared to true body ground).
4) If you have a pair of jumper cables clip one of the negative leads onto a mounting bolt/ground for the alternator and the other negative lead to the passenger strut tower ground/battery ground. If things improve (higher voltage/better running) you've found your problem. You can try cleaning all of the grounds to see if things improve. If not, try adding an 04 gauge cable from the alternator body/mounting bolt back to the passenger strut tower. That will ensure the body of the alternator is at true ground reference.

The PCM Control circuit has to have good grounds to operate properly. If it doesn't have the same ground reference at the alternator as that at the strut tower ground the output will be off (example would be if your water heater zero reference was 20 degrees off so instead of the water heating to 180 it only reaches 160. Same thing here - Results will be low output voltage.

Other related/contributing problems can be the battery cables themselves/fusible links and/or corrosion in the cabling and poor grounds/grounds need cleaning. This is obviously more of an issue in areas that salt the roads or humid/salt environments. Additionally, much of the cabling in our cars is 10 - 15 years old now however the main battery cabling is still available ($60 - 100). I replaced mine and saw my voltage output increase by 1.5v and that was after I added an extra alternator ground. Good luck.
 

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