What would make my voltage drop from 14 to 11

Tiny
CB60
  • MEMBER
  • 2002 CHEVROLET SILVERADO
  • 39,000 MILES
First I had the battery light flash in message center and voltage was at 14.7 and took to AutoZone and replaced battery. Light was off for one day then back on. Then next day voltage was at 14.7 and stopped and started back up and I noticed the volt meter went to 11 and stayed there. I took alternator out and had it checked at two AutoZones and both places showed it all okay. I checked alternator and battery with another volt meter to confirm this.
What can it be?
Do you
have the same problem?
Yes
No
Friday, December 2nd, 2011 AT 7:55 PM

15 Replies

Tiny
HMAC300
  • EXPERT
Check your grounds on left side of engine block and ground for ECM. The ECM tells the alternator to charge or not. Also, check the pink wires on the body relay box under left hand side of dash. As well as ignition 1 fuse. One other thing is to check the battery junction box for loose or cut wires near engine on left hand side.
Was this
answer
helpful?
Yes
No
+6
Friday, December 2nd, 2011 AT 8:13 PM
Tiny
CB60
  • MEMBER
Checked all grounds I could find, fuse, and battery junction box is okay.
Started up and went back to 14.7, but battery light in message center still coming on.
Was this
answer
helpful?
Yes
No
Sunday, December 4th, 2011 AT 4:53 PM
Tiny
HMAC300
  • EXPERT
Make sure your battery terminals are clean, if you have the side post type which you do the bolt gets corrosion behind it and does not make good contact. Other than that recheck the battery because they can have a bad one even if new. Otherwise you will need a tech 2 put on it and normally dealers only have that. Of course your gauge could be wrong as well.
Was this
answer
helpful?
Yes
No
Sunday, December 4th, 2011 AT 6:00 PM
Tiny
CB60
  • MEMBER
I know most people on here do not come back to tell your out come, and how will we ever know what works ! I kept checking grounds and everything else and all was fine so I decided to try a new alternator and belt from AutoZone even though the others checked out okay. So I put them on today and so far so good the battery light in message center went out and stayed out. I will keep fingers crossed and hope for the best. Thank you hmac300 for all of your ideas and Happy Holidays!
Was this
answer
helpful?
Yes
No
+4
Friday, December 16th, 2011 AT 10:10 PM
Tiny
WRENCHTECH
  • EXPERT
Your problem was intermittent from the start so any test would have been inconclusive.
Was this
answer
helpful?
Yes
No
-2
Friday, December 16th, 2011 AT 10:45 PM
Tiny
BUCKEYES
  • MEMBER
Okay, so my problem may be a little more involved, but I hope I can get some help. My voltage started dropping from 14 to 10 at times, causing the engine to cutout. At first I noticed mostly when maneuvering in the parking garage - braking and turning. Initially I thought maybe my battery (bought a new one), then the alternator (had it checked several times), then possibly a vacuum leak off the brake power booster. However, even when I just slow down and start turning the voltage will drop, then come back up to 14. If I am stopping at a red light, the voltage will drop (but not enough to cause the engine to cutout, yet!) And then come back up to normal. Any suggestions guys? The truck is a 2005 Silverado with a 5.3L engine (4WD) with about 75,000 miles. Any help would be great.
Was this
answer
helpful?
Yes
No
Tuesday, December 27th, 2011 AT 11:31 PM
Tiny
WRENCHTECH
  • EXPERT
This is most likely a bad alternator, but would require some in depth testing while the problem is occurring to eliminate all other possibilities.
Was this
answer
helpful?
Yes
No
Tuesday, December 27th, 2011 AT 11:36 PM
Tiny
HMAC300
  • EXPERT
The only thing I can think of here is to check the ground for the PCM as the PCM tells it to charge or not. It may be losing ground like in wetter weather and causing this. This is about the only thing I can think of unless the diode bridge in the alternator is messing up.
Was this
answer
helpful?
Yes
No
+1
Wednesday, December 28th, 2011 AT 12:06 AM
Tiny
CB60
  • MEMBER
Hey, I am back to offer a suggestion. My truck is still doing fine and I replaced alternator and belt as a chance it was the cause and both were original at nine years old. And I had mine checked out at two different places and they said it was okay. I have 39,000 miles on it. Seems to me it could very well be a slipping belt and or the alternator in your case. Belt is a lot cheaper to try first. Let me know what you find out.
Was this
answer
helpful?
Yes
No
Tuesday, January 3rd, 2012 AT 1:13 AM
Tiny
WRENCHTECH
  • EXPERT
It uses a spring loaded tension-er so if there are no frozen components or a bad tension-er, slipping is unlikely but would make a very loud noise if it was slipping.
Was this
answer
helpful?
Yes
No
Tuesday, January 3rd, 2012 AT 1:18 AM
Tiny
BUCKEYES
  • MEMBER
Update! (But still no solution). So after going over the whole thing myself, took it in for new brakes and tires, etc. The service guys were checking everything they could think of pertaining to the voltage drop, that actually was happening while they had the truck. We rechecked all the grounds, all good. We rechecked the battery and terminals, all clean and good, rechecked the alternator and voltage regulator, all checked fine. Cleaned the mass air flow sensor, all good. But the problem still persisted. The readout kept indicating just "low rpm" so no panel warning light and no specific code. We pulled off the TAC module and put a new one on, but no difference in reading (so we put the old one back on and saved $250.00). The fleet service guys have not ran into the problem so they could not offer any help.
This problem has only started over the past six months, but it seems the tachometer has been acting up for about a year and half (GM dealership will not do the cluster recall fix for some reason) so we can only get an accurate rpm reading with the machine.

Any new suggestions? Thanks guys.
Was this
answer
helpful?
Yes
No
-1
Thursday, February 23rd, 2012 AT 6:45 PM
Tiny
HMAC300
  • EXPERT
If this vehicle and is under a recall and the dealer refuses to do this, then contact GM and see what they say. They may send you to another dealer or not. But if it is under recall it should be fixed no charge. That can be your whole problem anyhow.
Was this
answer
helpful?
Yes
No
Thursday, February 23rd, 2012 AT 8:31 PM
Tiny
WRENCHTECH
  • EXPERT
There is not recall for a dash cluster on that vehicle and there never would be. Recalls are only made for two reasons, safety or emissions, nothing else.
Occasionally, they will have a repair defect so severe that they will voluntarily have what is called a campaign to repair something at no charge but there is not one of those for that vehicle either.
Was this
answer
helpful?
Yes
No
Thursday, February 23rd, 2012 AT 11:11 PM
Tiny
BUCKEYES
  • MEMBER
So after checking so many things, I came across this suggestion on another blog.

"There is a service bulletin for that problem on your vehicle. It involves two things. A software update for the engine controller and a cleaning of the throttle body."

Bulletin No: 04-06-04-040
Date: June 14, 2004
Subject:
Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body)

So the cleaning is no big deal and the guys at the first shop cleaned the mass flow air detector (since I have a K&N air filter they worried about the oil on those filters). The software update required a Tech2 so the dealership checked my current version and then updated the software for $120.00. So far no problems with the voltage or oil pressure dipping when breaking or making low speed hard turns in the parking garage or on the mountain switchbacks. I will keep an eye on it and if anything else develops I will be sure to let you all know. However, in this day and age of internet and email, it does not seem that it would be that hard to contact specific owners about recalls, software updates, or other safety type issues pertaining to their vehicles. Thanks for all the help guys!
Was this
answer
helpful?
Yes
No
+1
Saturday, February 25th, 2012 AT 6:00 PM
Tiny
HMAC300
  • EXPERT
Most companies if there is a software update will only do current year and not contact for anything further. Unless it is a specific recall.
Was this
answer
helpful?
Yes
No
Saturday, February 25th, 2012 AT 6:31 PM

Please login or register to post a reply.

Recommended Guides