Headlights flicker after alternator change

[dkad260]

2012 XL Denali, I lost my alternator driving the other day, went home pulled it and replaced it with an Autozone Gold.

Now when I'm driving at a steady speed, if I force it down shift and raise the RPM's, I'll get an occasional flicker of the headlights, if I put it in neutral and rev it, the lights won't flicker.

Nothing is loose.


Here's a quick video of my Torque screen, note the 15+V peaks, as well as the occasional peaks.

Definitely thinking about returning it and trying something else, unless there is another issue somewhere.

Thoughts?

 

[OR VietVet]

Sounds like it could be a failing diode in the alternator. I would swap that out.

 

[TexasGhoste]

2012 XL Denali, I lost my alternator driving the other day, went home pulled it and replaced it with an Autozone Gold.

Now when I'm driving at a steady speed, if I force it down shift and raise the RPM's, I'll get an occasional flicker of the headlights, if I put it in neutral and rev it, the lights won't flicker.

Nothing is loose.


Here's a quick video of my Torque screen, note the 15+V peaks, as well as the occasional peaks.

Definitely thinking about returning it and trying something else, unless there is another issue somewhere.

Thoughts?

Did they give you the correct alternator? I usually look at my RPO list just to double check. Those that work at Autozone sometimes just get you whatever they see in stock.

 

[Doubeleive]

it's under warranty swap it out, might not be the issue though. Be sure the output cable attached to the alternator is on properly.
how old is your battery?

 

[dkad260]

Did they give you the correct alternator?

I watched them pull it up, all the info matched what was on the screen.

I will take it back and try again.

Be sure the output cable attached to the alternator is on properly.
how old is your battery?

Yes, all is attached securely.

Battery is about 4 mos old, Flooded, not AGM, Duracell from Batteries Plus. Haven't had any electrical issues like this before the new alternator.

Very likely a dud.

 

[dkad260]

Here's the update, I replaced the new alternator with a new NAPA unit and the flickering at idle and while driving steady has ceased, voltage also remains pretty much constant.

The issue I'm having still is the random flicker when accelerating harder than "normal", like merging into traffic.

I can drive easy all night and it won't flicker, but lean into it and the lights will flicker very sporadically, no set pattern.

This I don't believe is the alternator, but maybe the current sensor on the NEG battery cable?

I didn't have these problems before, I would have noticed this much flickering.

Maybe one sequence of a dimming event but this is much more pronounced.

 

[mikez71]

If you think it's the current sensor, disconnect it and test! Then you can rule in or out the Electric Power Management.

Here's a thread that mentions it by disconnecting alternator plug.

Figured out how to keep steady voltage

on the 07+ we have this regulating system (Regulated Voltage Control or RVC) that basically controls the alternator when it sees more/less drain on the battery. Being that I have a decent sized stereo as well as HIDs (with the relay harness) on my truck, I looked for a way to turn the RVC off...

www.tahoeyukonforum.com

I know you say you didn't have problems until the alternator swap, maybe your battery took a hit when your alternator died?

 

[dkad260]

I disconnected the current sensor, the 3 wire connector on the battery NEG cable.

Lights still flicker on heavy acceleration, and while my volt gauge on the dash appears to be steady, here's a short video of what's going on.

Start of video I'm steady at highway speed, with a brief acceleration, then came to a red light. Once going again, I accelerated lightly back to highway speed then accelerated heavier and that's when I'm getting the surging at or just beyond 14.8-15V.

 

[mikez71]

Voltages are in operating range according to this info

Commanded Duty Cycle Generator Output Voltage:
10% 11.00 V
20% 11.56 V
30% 12.12 V
40% 12.68 V
50% 13.25 V
60% 13.81 V
70% 14.37 V
80% 14.94 V
90% 15.50 V

Charge Mode


The BCM will enter Charge Mode when ever one of the following conditions are met.
The wipers are ON for more than 3 seconds.

GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.

The estimated battery temperature is less than 0?C (32?F).

Battery State of Charge is less than 80 percent.

Vehicle speed is greater than 145 km/h (90 mph)

Current sensor fault exists.

System voltage was determined to be below 12.56 V

When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9?15.5 V, depending on the battery state of charge and estimated battery temperature.



Also saw this in owners manual...

----------------------
Headlamp Wiring

An electrical overload may cause the lamps to go on and off, or in some cases to remain off. Have the headlamp wiring checked right away if the lamps go on and off or remain off.
----------------------

I thought I saw some posts about headlight plugs burning up too, if it's not a fuse/relay issue maybe..?

 

[dkad260]

I know you say you didn't have problems until the alternator swap, maybe your battery took a hit when your alternator died?

It measures good, also less than a year old. Anything is possible, may worth having it load tested.

I thought I saw some posts about headlight plugs burning up too, if it's not a fuse/relay issue maybe..?

Headlights check out, wiring is clean.


There's something I left out and can't believe I did as I've done this 100 times before with no issues.

The day my alternator went out, I washed the Yukon. With all the pollen, I also misted the top of the engine. Not hardcore washing, just light misting pressure around the fenders and top of engine.

I didn't go anywhere for hours and moved it to another spot to clean the tires.

It wasn't until I was down the road I had my charging light come on and it was the original alternator.

Maybe a connector stayed wet, not sure where, I make it a point to not spray into the alternator but this is now the 2nd new alternator, same issue.

Sorry for not giving full disclosure but didn't think about it.

 

[dkad260]

how old is your battery?

I missed this, sorry, just under a year old.

 

[Doubeleive]

you might have got water in something that doesn't like it, I pressure wash mine a couple times a year and have for years and never had a issue
but you could poke around and check everything, if something looks questionable blow it out with compressed air and apply dielectric grease.

 

[dkad260]

I wanted to update this headlight flickering issue to say it has been solved.

I had re-checked all the connections at the alternator, grounding points, changed the belt (was old anyway) and this was where you could still see the voltage spikes which would coincide with the flickering on the new alternator from NAPA.

Voltage display on the Torque Pro app are as follows: on the left are from the OBD and on the right is the Command Module. I'm sure they are always the same but both were avail.

I ended up ordering a new AC Delco alternator from Rock Auto and this is what solved my headlight flickering issue. Voltages are pretty much rock steady at all throttle settings.

 

[petethepug]

Awesome news. Ty for the update!!

Lovely, something in the NAPA alternators was funk’d up. I was adamant that my service contract Admin only install an OEM alternator in our 08 Denali. Ultimately they gave up trying to get the GMC dealer to get a part store Alt.

The only reason they gave into a factory part is because I told them they’re responsible for my wife and kids if the alternator fails at 75mph on the highway at night. Scary they seemed concerned about that like they knew something I didn’t.