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Discussion Starter · #1 · (Edited)
I have an 08 Pontiac g8 gt that has about 134,000 miles on it. Within the last 6 months the headlights have started flashing. I've had the battery,alternator, and starter checked at Advance and all had good readings. The headlights, starter and battery are about 2 years old. I'm not sure how old the alternator is though and think that could be it even though it tested out fine. The battery gauge shows plenty of amps. We are completely baffled by this. I have a video of it doing this but I dont know how to post it on here lol! Any advice would be appreciated. TIA!
 

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Aftermarket headlights? What brand Alternator?, if not OEM our cars tend to not like them and cause all kinds of electrical gremlins.
 

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Discussion Starter · #3 ·
I'm not sure what type of alternator. I've had the car 5 years and when I went to have the battery replaced it was 7 years old lol! I honestly dont think the alternator has ever been changed. Yes they are aftermarket headlights but they have been in the car for 2 years and I never started having problems until 6 months ago. My motor seems to be running a little weird and almost sounds like it's running the way the head lights flash if that makes any sense.
 

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Check for codes? if it's running ruff there may be one, suggestion would be clean MAF and throttle body.
 

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Any other electrical related issues present? Check the battery and alternator connections along with the battery ground bolt, Battery ground bolt
 
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Discussion Starter · #6 ·
There's no check engine light or any lights on the dash but the tpms light. We have cleaned the battery connections and checked everything we can see. My locks stopped working but not sure that's electrical. I don't know of any other electrical problems atm. It just passed inspection today. If there isn't any warning lights on will a code reader even tell me anything?
 

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Discussion Starter · #7 ·
I wish I could post a video of it. The headlights stop flashing when it is coasting or in park. They only flash while I'm driving it. Makes absolutely no sense to me. The battery is reading between 12 and 16 on the gauge.
 

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When the headlights flash any other interior lights flashing? Display ,radio, dome lights if on, if you do a WOT pull does your cluster stop or go blank?
 

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Discussion Starter · #9 ·
The mph, rpm needles are kinda flashing but not enough to notice like the headlights.None of the other lights like the radio or dome lights flash. I also just thought of this but the ac blower will go low like someone cut the fan down and then go back to normal. It has done that several times and did it continuously when we were driving back from Tennessee. It would kinda pulsate like the headlights were. I thought maybe my belt may be slipping. I'm far from a mechanic though lol! Also I'm not sure what a WOT is haha!
 

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WOT is short for Wide Open Throttle, so if you punch the gas peddle all the way down curious to know what your gauges are doing, thinking you may be having Volt spikes?
 

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Discussion Starter · #11 ·
All I can tell you is when I'm driving down the road the ac and the headlights pulsate. The rpm gauge looks to be normal and so does the mpg gauge when in full throttle. We were driving last night on the interstate going about 75 mph though and every now and then we could feel like a quick hesitating type feeling and then it was normal. Like a 1 second loss of power and then normal again. It's so hard to describe. I'm sorry it sounds so confusing 😥
 

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The battery ground bolt is located under the car on the driver's side. Presuming the alternator connections were checked, check the wire going from the positive engine jump post to the alternator. Depending on the equipment, a battery, starter or alternator can test good and still have an issue(s). A good on board diagnostic tool scans for both pending and current codes. Typically, a pending code does not illuminate the check engine light.
 

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Discussion Starter · #13 ·
Ok we will definitely check those next. One more thing though. Would all of this make the transmission start slipping? It just started in the last few months as well. I didnt mention it before because I wasnt sure if the two could be connected to one problem. I just thought the transmission may be going out. We have never changed the fluid until about 2 weeks ago since I've owned the car. My boyfriend says you never flush an old transmission but he was also afraid to change the fluid because he always heard the transmission fluid was to be the lifetime of the car. I was so aggravated with him over this though lol! He will not let anyone else work on my car haha! That's why I'm here to get more opinions. I thank you both very much for giving me advice and appreciate it more than you know.
 

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Definetly need to get a good scanner on it. On the transmission ,that's what mine was doing but I was at 210,000 miles,we rebuilt transmission and replaced valve body seals, I wouldn't flush it either but definitely change fluids and filter 75,000-100,000 miles. On the the lights flashing, you had mentioned your Volts had gone up to 16, seems a little high, if it's doing it at higher RPM'S seems like it's making to much juice and the BCM is trying to protect itself and shutting things off? May be totally wrong but that's what fixed my similar symptoms that your having.
 

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I wish I could post a video of it. The headlights stop flashing when it is coasting or in park. They only flash while I'm driving it. Makes absolutely no sense to me. The battery is reading between 12 and 16 on the gauge.
So it sounds like as soon as the car is under increased electrical load that these issues appear hence not when coasting or idling when there is far less load on the alternator. Increased load is demanding increased current from the alternator. With a bad connection especially to frame that will cause increased resistance therefore inhibit the extra current trying to flow and could be causing a fluctuating problem.

Presumably everything is fine when the engine is not running (therefore alternator is not running) therefore the headlights are running from the battery and not pulsating on and off.

It comes back to the Alternator itself but more likely the "voltage regulator" in the alternator and this may also have brushes which are worn. The other posts suggests checking the ground point which is where the negative lead leaves the battery in the boot and bolts hard to the frame. There is also a current sensor there. Its a round piece of plastic (which is a coil of wire) which the negative cable passes through before it bolts onto the frame with some signal wires coming from it. They are known to go faulty.

So

1. Check alternator again and that others have posted ENSURE it is GM or AC Delco specifically for that Car and not an aftermarket as they are not compatible with the G8 electronics.

2. Check the ground point between the negative lead from the battery and the frame of the car

3. Check or have checked the Battery current sensor located around that cable.
 

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Discussion Starter · #16 ·
Yea we checked the DIC this morning on our way to work and the battery is only charging to 85% overnight. Not sure that means anything but the volts were reading at 14.4. My boyfriend says it's definitely getting a charge good enough so I'm not sure if that tells you anything but just thought I'd mention it. It also seems to shift better in manual so we are currently driving it in that mode. We tried to drive it in sport mode but it shifts to 6th gear going at only 45 mph which we're not sure that's normal. Also when at a stop in manual it only goes down to 2nd gear not 1st which we thought was strange too. You guys are all great and whatever the case may be with it I will be sure to update on what we find and let everyone else on here know in case they come across some similar issues. There isnt very many places for us to ask about these cars so I'm definitely going to try all of your suggestions. I just wish it would finally show me what it is and make it easier lol!
 

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You are losing voltage from either bad connections or an alternator regulator that does not keep up with loaded demand, easiest is first turn on everything like high beams rear defroster and a/c, measure the voltages at alt rear stud of alt. then at jumper post under hood then to pos battery post there should be no more than half a volt difference between them, then monitor voltage from aux outlet while this happens you will see it drop voltage, for grounds use a dvom on voltage setting between ground at battery and ground at ground post under hood and engine block there should be no more than half volt there also. any zig zag fluctuations in voltage will point to alt
 
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OEM or AC Delco, look on RockAuto, dont forget to look up coupon code for 5% off.
 
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