Follow Pontiac Owners,

I have a 1999 Bonneville, SLE, non-SC.
Here is my Issue:
When I first start the car, I have almost 14 volts at the Battery, as the car warms up, the Voltage slowly drops to 13.5. This seems normal. However, as I increase the load (A/C, Headlamps) the voltage drops below 13 volts. The kicker, when I shift out of Park, voltage spikes downward below 11 volts, sometimes below 10 to the point where lights dim and Accessories begin to drop in efficiency. I began by disconnecting the Daylight Running Lights, this seemed to improve the loss of Voltage, but, a significant loss in voltage remains and the Alternator seems to have a very difficult time keeping up.

What has been done:
New Alternator
New Belt Tensioner
New Belt
New Battery
DRL Disabled

I need some hints/directions on where to go to solve this issue.

Corrosion could also contribute to voltage drop. Look for it at the terminals, and also within the large gauge cables.

Thank you for replying.

Terminals at Battery, clean. Terminals at Firewall FuseBox, clean. Terminals at Alternator, clean. Terminals at Starter, clean.

Largest Voltage drop is at the Point when I Shift from Park. Especially, when Engine is at or near Running Temp. Voltage drops 13.5 to 11 volts or less and does increase, but only to just over 12.

Main Line from Battery to Alternator: I peeled back the Black Tape and Removed the Plastic Corrugated Cover. I found a 3/8 inch gash in the wire insulation. The Copper Wire did not seem to be damaged, no evidence of arcing.

Have you had the alternator load tested? Just because you replaced it doesn't mean it'* not defective. Take it to a place like Auto Zone and have them load test the battery and alternator for free.

I purchased the Alternator from AdvanceAuto, and as a Routine, I had them test the Alternator before I left the store.

I had them test my alternator ON my car. Maybe you have something wrong with the wiring.

Okay, Let'* try this again. DRL'* are Disabled.
At start up, 14 plus Volts cold, at Running Temp 13.65 - 13.7.
At Running Temp, Only Lights On, 13.65 - 13.7.
At Running Temp, Only A/C (coolings fans On)On, 13.5 - 13.6.
At Running Temp, Lights and A/C (cooling fans On) On, 13.45 - 13.5.

At Running Temp, NO accessories Running, Shift from Park, 13.65 - 13.7
At Running Temp, Only Lights On, Shift from Park, 13.5 - 13.60
At Running Temp, On A/C (cooling fans On), Shift from Park, 12.6 - 13.0
At Running Temp, Lights and A/C (cooling fans On), Shift from Park, 10.5 - 12. Want to Stall, Voltage slowly climbs to steady around 12.5 volts.

Why is this an issue? Is the battery dying and won't start the car? Aside from your concern over the voltage readings, and you experiencing any problems that lead you to believe the charging system is not functioning properly?

The Battery is not Dying, the car Starts every time. Could I have a Torque Converter issue? Could one, or more of the Electronically controlled Solenoids cause the Transmission to drag, either because they do not get enough Voltage or they themselves are creating a Drain?

When the Voltage drops into the Red, the Lights Dim and the Accessories (A/C) in particular, almost cause the car to stall just by putting the car in to Gear, I simply believe that it is cause for concern. There has been only one occasion when I had come off of the highway, drove several blocks, and as I was making a right hand turn, she came to almost stall and I lost my Power Steering. The Voltage dropped into the Red. I do not want a repeat of that instance, it could happen when it could cause an accident.