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Dropping voltage at idle. (Kinda long read)

JLM09LTZ

Full Member
Joined
Feb 25, 2016
Messages
28
Location
Cleveland, OH
Not sure if this as been covered completely or not but here's the deal, my 09 Avalanche LTZ 5.3 Flex Fuel has been having weird intermittent electrical issues for about a month now. It all started when I noticed it would hesitate whenever I went to turn the key and start it up. Almost the same click sound synonymous with a failing starter. Later that day, the truck went into total flip-out mode. The door locks were jumping up and down, the dash lights went nuts, the truck would come out of drive and back in without shifting the gear lever, seat belt chime was singing and so on. I scooted the truck back up my driveway and as soon as I turned the key off, everything died. Popped the hood, wiggled the battery cables and it came back to life. I put a quarter turn on the battery terminal nuts and the truck seemed to be fine after that. I drove it 80 miles that night, no problem. Fast forward a week or so, as I was driving, I noticed whenever I hit the brakes, the headlights flickered. Then I started noticing that the voltage gauge was dropping severely at idle with the brakes applied, I'm talking below 12v. So naturally, I'm thinking the alternator was going bad and maybe that's been the issue the whole time. I replaced my original 145amp with a brand new Delco 160amp and replace that braided ground strap next to the master cylinder with a new cable. Test drove it that evening and everything seemed ok. Fast forward to last week, we got a pretty good heat wave here in the Cleveland area and I had the A/C kicking. I would notice again that the voltage would drop dramatically at red light with the A/C on, but whenever I turned the A/C off, it would be in the normal fluctuating range (within spec of the economy mode voltage drop). This past weekend, I had to drive it to Cincinnati and again it was hot. It was fine for about 2 hours in but then I began to notice that every time I hit the brakes or turned on my turn signal to change lanes, the radio would cut out. This time, it was happening while moving 75-80mph. Driving in Cincinnati and on the route back home, I decided not to risk it and I ran without the A/C on at all. Everything was good. Fast forward to Today, I'm in line at Wendy's, no a/c, no phone charger plugged in, nothing and the voltage dropped so low that the radio cut out and the dash lights and seat belt chime activated as if someone just turned it on. I'm beginning to think I may have a bad computer or something. I'm trying to figure this out before shelling out a ton of money to a shop. Has anyone had this issue?? Does anyone have any ideas?? I will literally try anything at this point.

Just some info on the truck:

-2009 Avalanche LTZ 5.3 flex fuel
-184,000 ish miles
-Every major component is original minus the belt, battery and alternator, and a few miscellaneous parts like the drivers side engine mount, front end components etc..
- The truck gets oil and filter changes religiously every 4000 miles and I only use Delco oil
- Most importantly, it has no added on aftermarket electrical accessories what so ever
- It does however have pretty much every electrical feature GM offered like the Bose system with rear screen and navigation and the power running boards, auto wipers, heated and cooled seats, etc
-No tow package though

Pleeeeez!! Any help would be greatly appreciated!
 
Whenever my car does something like that, which it has I always clean the battery terminals both negative and positive. Nothing like a loose terminal to give you the blues. Clean your MAF and throttle body also for idling problems.
 
You might want to get a Priest and do an Exorcism.  Had something like that happen to my Burb.  1996.  Shut off at red lights.  Meter would drop.  It was the passenger side vanity mirror pulling power.  The tiny shut off button was broken. But I dont know.  That's alot of stuff happening.  Good luck.
 
I would have:
battery charged properly off truck and tested
Alternator tested
Starter tested
inspect all ground wires
inspect fuse box for mice chewing on wires.
Heck inspecct all wires for mice chewing on wires - them critters love insulation.
Check battery cables from battery all the way to alt and starter
 
Since you mentioned tightening the battery cables, I agree with cleaning the posts and connectors for the battery.  Follow the cables all the way to the end to make sure they're OK.  If that doesn't work go the mouse route mentioned above.
 
I will definitely test the battery and alternator. The battery was purchased from Advance in November 2017 so its not terribly old. The alternator is about two weeks old. everything in me is saying that this situation is from a bad alternator. I ordered a new OEM Delco ground cable from the battery so I will replace that tonight when I get home. maybe I should order the positive cable also just to eliminate that as the problem. Does anyone know of any exorcists??  :help:   
 
no sense replacing cables unless they are bad...

New Alternators can be bad and so can battery.
 
I have had batteries go bad in less that two years.

Take it and have it LOAD tested, to be sure.

I have had a couple of alternators be bad right out of the box.

Never worked once.

It happens.

(n)
 
So I'm currently sitting in the Avalanche, engine running, A/C on full blast. If I put it in drive and hold the brake, it flips out. Voltage dropped to just above 9 volts. Itll sit there for about 10-15 seconds, act like it's going to cut off and then all of a sudden it'll jump back up to 14v and run normal. In park, it'll be fine for a while. Foot off brake pedal or on brake pedal and it'll sit and idle at 13.5v to 14.3v only dropping to 12.7v when the fan kicks on. (I'm testing with a multimeter at battery terminals. Im getting ready to rip the alternator off and take the battery out and have them tested.
 
It's probably time to have both the alternator and the battery tested. The battery should keep the voltage above 12 volts.
 
UPDATE: It was/is the fan. The whole time I wasn't paying attention but whenever the condenser fan kicks on, the voltage goes to the floor. Any other time that the condenser fan is not on, regardless of the low speed fan operation, the voltage is fine.
 
Did the battery and alternator test good? The fans draw a large load and would expose a failing battery, alternator or wiring.
Advance, Autozone, Oreilys and probably others will test your battery and alternator for free, no removal necessary.

You may have already done this though
 
Battery and Alt both checked out fine. I actually just went on and made them warranty out the Alt since I just got a new one when all of this started going on. So far I have replaced both the positive and ground battery cables, and the alternator (twice) and tested the battery. All seems well until the fan kicks on. Is it possible for the fan to be internally shorted and drawing too much power?
 
JLM09LTZ said:
Battery and Alt both checked out fine. I actually just went on and made them warranty out the Alt since I just got a new one when all of this started going on. So far I have replaced both the positive and ground battery cables, and the alternator (twice) and tested the battery. All seems well until the fan kicks on. Is it possible for the fan to be internally shorted and drawing too much power?

Possibly, but I would expect the fan to be non-functional. Have access to a clamp ammeter? You could measure the current going to the fan  https://www.amazon.com/Auto-ranging-Digital-Clamp-Meter/dp/B001VGND88
 
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