Today I couldn't start my car. I jumped start the car, and the voltage meter was reading at 12V. While I was driving, the voltage started to drop slowly to around 10V, then 8V. I drove for about 4 miles, and shut off the car. Now the car won't start. Is it the alternator or battery problem? I changed the battery like 2 years ago, and I daily drive the car.

Please advise.

 

Also, for a few months, I have to turn off the radio and air conditioner before shutting down the car. Otherwise car won't start.

 

I had exactly the same problem earlier this week. Car was just acting strange. First off, I threw a PSM and ABS lights driving one night. Turned the car off and on and PSM and ABS lights went away. Read the codes. Ton's of them. Cleared them all. Car started idling funny. Next day, car would not start...click,click,click. I needed a new battery anyway, so I just replaced it. Car started, but after driving I noticed I was running 12v. The next day it started over charging - 14-15.8v. Turned everything on (heated seats, high beams, a/c - got the volts under control and limped home. Had a new alternator installed. Car is running perfect. Bad alternator can impact a lots of components.

 

Alternator.

 

Cool. Thanks, just ordered an alternator from Autohauz for $300, better than dealer for $1500.

 

If you got access to a voltmeter you can do this simple test:
Start Car and run at a normal idle.
Connect a Voltmeter Directly Across the battery Terminals.
Turn on Headlights to High Beam.
check the battery Voltage.
The Battery voltage Should read between about 13.8 to 14.2 volts. (Possibly up to 14.5 Volts.)
Increase motor speed to about 1500 RPM. The Alternator should now produce a battery voltage between 14.2 and 14.6
Volts.
If it is Lower than 14 volts, the Alternator probably has one or more Bad Diodes.

 

or you can spend $40 and replace the regulator. At least I know how many miles the alternator has on it. Most rebuilders just repair the problem, test it and its gone. The bearings could have 80k on them.

 

Any detail how to find $40 regulator?