Chevy and GMC Duramax Diesel Forum banner
  • Hey Everyone! Vote for the Site Favourite ROTM winner for the year of 2021 HERE!
1 - 20 of 32 Posts

·
Registered
Joined
·
435 Posts
Discussion Starter · #1 ·
This is a weird one for me.

A few days ago I hopped on the interstate around dusk and I immediately noticed my headlights were a bit dim and seemed to flicker occasionally. Glanced down at my dash gauges and the battery voltage gauge was hovering at 12. Not charging it would seem. I flicked through the CTS3 and it confirmed the same.

Not wanting to pull it over and shut it down and risk an expensive tow I just rode it out to see if it would come back up. I tried running with all unnecessary electronics turned off and no change. So then I turned on everything I could to try and see if a big load would get the alternator charging again. No change.

I get off the interstate at my exit and as soon as I start slowing down my voltage starts to rise. Sitting at a dead stop I'm charging at 14.0 volts. Not what it normally charges at (14.3 to 14.7) but better. It's been brutally cold here the past few days so the truck has sat but next week is warming up so I'll be back to work and I'll need my truck for that.

Anyone experienced this before? I've only ever had one alternator go bad and that was on a gas truck and it just plum quit one day.

Any suggestions on diagnosing it to ensure it is the alternator at fault? I'm about 99% certain it is but I hate throwing parts at problems and it's always good to learn new diagnostic techniques. Especially electrical ones because those are not my forte.
 

·
Former GM Tech and parts
Joined
·
3,201 Posts
Similar, but pretty much the opposite happened to me a few years ago. Road trip to the other side of Illinois from home to pick up some parts, going down the interstate the battery light popped up and went off before I could see what it actually was. Did it a couple times before I figured out it was the battery light. Thought I'd hop off the interstate to stop at a parts house and get it checked- kicked the cruise off and it dropped to battery voltage only. Stopped at the parts store, ripped off the alternator and took it in to test- sure enough wasn't charging high enough to pass. Installed a new one and rolled on.
I would suspect alternator for sure.
 

·
Registered
Joined
·
243 Posts
You can get the alternator tested for free at any chain parts store. Sounds like it may be failing with that kind of intermittent performance. Get the batteries load tested at the same time to check their function.
 

·
Registered
Joined
·
435 Posts
Discussion Starter · #4 ·
You can get the alternator tested for free at any chain parts store. Sounds like it may be failing with that kind of intermittent performance. Get the batteries load tested at the same time to check their function.
Yes, that's probably my next step. The batteries are relatively new and the "Battery Not Charging" message never came up on the dash. The truck started up like normal the next morning after sitting 12+ hours overnight so I don't think I depleted the batteries but I intend to have them tested and put them on the trickle charger before putting the truck back on the road.
 
  • Like
Reactions: scottydl

·
Registered
Joined
·
435 Posts
Discussion Starter · #5 ·
Similar, but pretty much the opposite happened to me a few years ago. Road trip to the other side of Illinois from home to pick up some parts, going down the interstate the battery light popped up and went off before I could see what it actually was. Did it a couple times before I figured out it was the battery light. Thought I'd hop off the interstate to stop at a parts house and get it checked- kicked the cruise off and it dropped to battery voltage only. Stopped at the parts store, ripped off the alternator and took it in to test- sure enough wasn't charging high enough to pass. Installed a new one and rolled on.
I would suspect alternator for sure.
What happened to yours is what I would expect a failing alternator to do. Charge when under a decent load and not charge when under little or no load. That's what has thrown me for a loop on this one. Seems completely counterintuitive.
 
  • Like
Reactions: DMAXfirefighter

·
Registered
Joined
·
86 Posts
You can get the alternator tested for free at any chain parts store. Sounds like it may be failing with that kind of intermittent performance. Get the batteries load tested at the same time to check their function.
This is good advice.
 

·
Registered
Joined
·
1,876 Posts
Also - check your chassis grounds and inspect that you dont have any crazy corrosion on your battery terminals. Get some water and rock salt kicked up and it could get messy quick
 

·
Registered
Joined
·
435 Posts
Discussion Starter · #8 ·
Okay, it's definitely the alternator. I've read a bit on here and was just wondering what y'all recommend for a replacement? I've seen some upgrade to the XDP but I'm not a huge fan of buying parts that can't be obtained locally in a pinch. I will buy parts like that if it's a serious upgrade but otherwise I just run down to the local parts house and get the best I can afford. O'Reilly's carries "new" Optimas as well as remanufactured AC Delco units. What do y'all think is best bang for the buck?
 

·
Registered
Joined
·
86 Posts
I grew up with my dad insisting on rebuilt starters and alternators. I cannot really say we had much trouble with them but I have always bought new replacement parts for my vehicles. So, in a way I guess I am saying I don't think you can make a bad choice here unless you go with some off brand, etc. I would stay away from anything Optima.
 

·
Registered
Joined
·
4,711 Posts
Where and how you get a replacement warranty part if need is always high on my list of what to replace something with.
 

·
Former GM Tech and parts
Joined
·
3,201 Posts
I've never liked AutoZone for electrical stuff, but that was what I had in my situation needing an alternator that time so I used theirs. A few months later that replacement failed, but they gave me another one. Still running that one today
I usually use Napa or Oreilly personally
 
  • Like
Reactions: sumyunguyz

·
Registered
Joined
·
243 Posts
I can’t remember the brand name but I had problems with the cheap Advance Auto reman alternators. I went through 3 of them in a 2-3 year period on a previous vehicle (95 gas Suburban). Yes they were always under warranty and fairly easy to swap out… once in the Advance Auto parking lot… but it was a pain to deal with and I almost ended up broken down & stranded 2 of those times. And I think the failing charge ruined my battery 1 of the times too.

If reman AC Delco is an option, that sounds like a pretty good blend of value + better reliability. Depending on the price difference between reman & new.
 

·
Registered
Joined
·
1,876 Posts
Around here we have a shop that actually re spins alternators. They do upgrades as well when they crack it open. Not sure if thats an option by you but that way they can up your amperage a bit as well.
 
  • Like
Reactions: DuramaxNWA

·
Super Moderator
Joined
·
1,743 Posts

·
Registered
Joined
·
435 Posts
Discussion Starter · #15 ·
  • Like
Reactions: viper8315

·
Registered
Joined
·
435 Posts
Discussion Starter · #16 ·
Around here we have a shop that actually re spins alternators. They do upgrades as well when they crack it open. Not sure if thats an option by you but that way they can up your amperage a bit as well.
I've tried looking around my area for a rebuilder but haven't found anything yet. I'm in SW Missouri so if anyone knows of a good rebuilder I don't mind making a drive for a quality rebuild job.
 

·
Premium Member
Joined
·
458 Posts
Seems like it’s the time for alternators to fail. I just replaced mine. Advanced auto.
 

Attachments

·
Registered
Joined
·
435 Posts
Discussion Starter · #18 ·
Seems like it’s the time for alternators to fail. I just replaced mine. Advanced auto.
It's weird how these things tend to go in groups around the same time. A friend of mine with a similar truck called me last night and mentioned his alternator was acting up, too.
 

·
Registered
Joined
·
86 Posts
It's weird how these things tend to go in groups around the same time. A friend of mine with a similar truck called me last night and mentioned his alternator was acting up, too.
Bad batteries and alternators show up now in the dead of winter. Sometimes you chase the trifecta of battery, alternator, or regulator. Good luck.
 

·
Registered
Joined
·
1,876 Posts
Bad batteries and alternators show up now in the dead of winter. Sometimes you chase the trifecta of battery, alternator, or regulator. Good luck.
Shhh dont you wish that on me Ricky Bobby!
 
  • Like
Reactions: BlownL36
1 - 20 of 32 Posts
Top