Replaced alternator 2 years ago with rebuilt Bosch. Since then have had no problems though voltage meter is usually about 3/4. Last few days, voltage is almost pegged and today the small battery light came on. No crazy audio or anything else, (I know boring).

Ideas?

 

Pegged usually means full bore.... is it overcharging or undercharging? Have you checked the voltage at the battery with a voltmeter when the engine is running?

 

Don't have a voltmeter, will have to take to Autozone I guess. Battery light comes on when I slow down.

 

It only comes on when you slow down? You really need a voltmeter to diagnose this, but if its intermittent you might want to check the tension on the serpintine belt, if its loose it could be slipping over the pulley. Try turning on the A/C compressor and see if you hear it squeal and if it immediately turns on the battery light by adding a little load.

 

I checked the battery with a battery charger and when I checked with engine off, it was about 10 on the chargers meter. I started the car and it was about 4 on the chargers meter. I also noticed when I turned on the AC w/o revving the engine the cars voltage gauge drops to about 13 and the lights dim. If you rev the engine to 2k the lights come up and the gauge goes to about 15.5.

Battery or Alternator?

Also what is the difference between the Bosch and Valeo units?

 

If the car starts the battery is fine, its the charging system thats the problem. Can you verify what a loose belt? Try pulling on the belt, if you can manually lift the belt almost off the alternator the tensioner is shot.
If thats good the charging system needs to be diagnosed, take off the alternator and take it to autozone (or whoever) to verify its working correctly. If its not, you need a new alternator, if it is, further diag needs to be done with a voltmeter that i don't think you're qualified for.

 

Sounds like the regulator in the alternator is going out, see if you can get a warrantied replacement

 

Checked the belts, seem tight. Will have the alt check tomorrow.

Thanks for the help!

 

What did you end up doing with your car? Mine have the same symptoms.

I havent done any diagnostic test yet (too freaking cold outside), but my voltage meter(on the dash) drops to 12V when I have my HVAC and rear defroster ON. The voltage meter climbs up close to 14V when i rev the engine. My timing belt was replaced 2-3yrs ago.