Doing research after the fact, I found out our cars control the alternator output to two different voltages depending on conditions, which potentially lead me to replacing a good alternator...



Link below

http://www.google.com/url?sa=t&rct=j...bv.97653015,d.


Kind of long story, but, 2 days before a 2000+ mile road trip, I hear a whining noise from the engine bay. It lasted most of a short round trip maybe 5 miles, then went away. I thought I may have seen something weird with lighting too during that time, but never got a warning message. Everything seemed ok the next 100miles though. I was thinking alternator might be starting to have some issues, and read some other posts/saw videos about whining from a bad alternator.


To be safe I bought a reman alternator from advance auto parts and brought it with me on my trip, with some tools.

On the road trip, after arriving at first destination (@400miles) and driving around town a bit, I thought I noticed some funny things with lighting and there was some slight whining noise, I checked voltage and was in the 12v range sitting parked at idle (don't remember if ac was on or not), so I thought for sure it was going bad. Still no warning light. I replaced the alternator with the one I brought, didn't take too long. Voltage seemed ok after that ~13.9v

Continuing the road trip, the new alternator started giving me a quick check charging system warning light flash, at high rpm 6k+, and a couple other quick flashes when I was driving with the ac off (ac is on 99% of time, just had windows down to enjoy weather at request of a passenger). When checking the voltage, I noticed it was dropping to 12.3 with ac off, and would go back to 13.9 with ac on, so thought the new alternator definitely had weird problems.


Back from my trip, I research more and find this dual mode thing, so I'm not 100% sure my original alternator was bad. I definitely think it was making noise, but not sure if my voltage readings were right.


Today I exchanged the reman alternator for another one and installed it. I did a little test drive with ac on/off and different speeds and whatnot, and the voltage definitely changes and overall what I expected now after reading about this dual mode operation. My voltage now is ~14.4v in hi output mode and ~12.7v in lo output mode. This is still about 0.5v higher than the last reman alternator, so that's good. Haven't done any high rpm runs yet, but I hope this one doesn't give me a check charging system light too :/



So I guess kind of an FYI post that the alternator can put out "low" voltage and be working perfectly fine, it's new to me

 

New to me too. Thanks for sharing.