2006 Pontiac Montana about 148,000 miles. Voltage readout is erratic. Varies from 15.3 down to 12.8. Got ABS and stability control warnings that came and went. Replaced battery which was old, did not help. My mechanic replaced the alternator, but I still have the problem, except don't get the warnings. Any thing else to try?
Varies from 15.3 down to 12.8.
those are all within specification. The computer modulates voltage to manage the charging system.
If you have no charging system warning light, then it's working as intended.
Got ABS and stability control warnings that came and went
A diagnostic scan must be performed to retrieve the fault information that set the warning light.
My experience with my GM cars, the onboard voltage displays a 1 whole voltage higher than actual. Get a good voltage reader to determine. Both my code reader and volt meter match other and thats how I figured out a faulty alternator. And newer GM's need an ac delco to function properly. Aftermarket seem ok but underperform under load.
