high charge voltage causing LED Headlights to Flicker

[_LeO_]

Hi all, new here.

i've been having an issue with my aftermarket LED headlights flickering and dimming for the past few months while braking on my 2019 GMC Canyon Denali. originally i thought it was just a bad bulb since it was only a single bulb on the driver side, so i contacted the place i bought them from and they sent me a new set of Morimoto 2stroke 4.0 under warranty to replace the 3.0s i had for 2.5 years. voltages from the battery and alternator seemed good through the charging system and the resting battery voltage while a little low was still sitting above 12 volts

while waiting for the new lamps to be shipped to me my alternator died, had that replaced but still the headlight issue persisted. once i got the new lamps things got a little worse, at least worse from what i noticed. flickering persisted but for the first few minutes of start up these lamps would dim and flicker randomly from both headlights while driving and not just braking like i was noticing before. upon further investigation of my voltage, i noticed my starting voltage was running at 15 volts for a few minutes before settling down and staying at a steady 14.4-14.5 volts at times it would spike to 15.5 volts for a few minutes. would rarely get to below 14.4 volts.

thinking it was a load issue, i replaced the battery, given that its 5-6 years old i figured it was time to replace it, but still no difference, my mechanic replaced the alternator again thinking that the new one could be a faulty, same issue. did some diagnosis, disconnected the communication connector for the alternator and the voltage dropped to its default output for the alternator. thinking it was a grounding issue, we jumped the alternator to the negative battery and it seemed to do something, so we ran a #4 ground from the alternator to the negative battery terminal. the voltage dropped a little bit for a few days and at a normal voltage of 13.9-14.2 the headlights ran normally, and now the voltage has been back to the same figures and the headlight issues still persists. i guess the lower running voltage was just there until the BCM/ECM re-calibrated to the new ground

at this point we are thinking the problem could be a failed current sensor not relaying the right load back to the BCM which is calling for a higher voltage, but would this cause the headlights to flicker? the current sensor only comes with the negative battery harness and to completely replace the harness is not an easy job on these trucks, looks like the fuse box in the engine bay has to come out and the negative that mounts to the block sits above the front differential and is a pain to get to.

anyone here have any thoughts or opinions/ recommendations to check? has anyone seen such a thing?

i should also not, that when braking the dome lights would also dim for a half second but given that they aren't LED they are not as reactant as the driver/ballast on the LED bulbs.

i'm also an electrician by trade, the only issue is i'm not fully familiar with the system controls in a vehicle, so troubleshooting without fully knowing the order of operation is a little more difficult and i need to do a bit more research on the systems structure so any help would really be appreciated

 

[Marcozi]

What is the "new" alternator? Is it a rebuilt or new? What brand is it?

Modern vehicles usually have some sort of charging management software. Where? So the manufacturer can eeeek out an additional 0.05mpg. Basically, the software stops the alternator from charging under certain conditions. Those conditions vary by manufacturer. I would also check grounds, especially the engine to chassis ground cable.

 

[mk378]

Yes that is smart charging. It runs barely enough charge most of the time but when there is mechanical power to waste such as rolling downhill or braking it drives the alternator hard to catch up the charge in the battery.

LED bulb systems should be able to handle 15 - 16 volts. The LED itself runs from a power converter not direct from the supply.

 

[Rand]

Inserts obligatory "aftermarket led lights you are one of those guys" comment.

 

[eljefino]

Yeah those aftermarket headlights sound like the problem. If you want to kludge this you might be able to add diodes that cut half a volt.

 

[Thermo1223]

Take a look. I don't think much has changed since they implemented it. My interior lights dim and do some weird things but my LEDs in my headlights never gave me an issue but they have their own regulator/driver.

https://thegrouptrainingacademy.com...d2f8c78fefd195e17c4_LBT142-GM-SMARTCHARGE.pdf

 

[AZjeff]

Still have the OEM parts? If you put them back in and the problem goes away does it tell you anything?

 

[Cujet]

anyone here have any thoughts or opinions/ recommendations to check? has anyone seen such a thing?

Of course. Many LED bulbs have drive circuitry that regulates power (voltage/current) to keep the LED at a constant brightness. Take a cheap LED flashlight bulb and slowly ramp up the voltage on a bench top power supply. What you might see is a stepped increase and decrease in brightness as you raise the voltage, and maybe even specific voltages were the bulb simply won't illuminate correctly. That is due to poorly designed regulation.

I'm not claiming this is what's happening with your setup. But it does seem there is some form of incompatibility there.

Just an FYI, I've had the best results with LED headlights from Beamtech, but only their brightest, most expensive offerings.

 

[wag123]

Hi all, new here.

i've been having an issue with my aftermarket LED headlights flickering and dimming for the past few months while braking on my 2019 GMC Canyon Denali. originally i thought it was just a bad bulb since it was only a single bulb on the driver side, so i contacted the place i bought them from and they sent me a new set of Morimoto 2stroke 4.0 under warranty to replace the 3.0s i had for 2.5 years. voltages from the battery and alternator seemed good through the charging system and the resting battery voltage while a little low was still sitting above 12 volts

while waiting for the new lamps to be shipped to me my alternator died, had that replaced but still the headlight issue persisted. once i got the new lamps things got a little worse, at least worse from what i noticed. flickering persisted but for the first few minutes of start up these lamps would dim and flicker randomly from both headlights while driving and not just braking like i was noticing before. upon further investigation of my voltage, i noticed my starting voltage was running at 15 volts for a few minutes before settling down and staying at a steady 14.4-14.5 volts at times it would spike to 15.5 volts for a few minutes. would rarely get to below 14.4 volts.

thinking it was a load issue, i replaced the battery, given that its 5-6 years old i figured it was time to replace it, but still no difference, my mechanic replaced the alternator again thinking that the new one could be a faulty, same issue. did some diagnosis, disconnected the communication connector for the alternator and the voltage dropped to its default output for the alternator. thinking it was a grounding issue, we jumped the alternator to the negative battery and it seemed to do something, so we ran a #4 ground from the alternator to the negative battery terminal. the voltage dropped a little bit for a few days and at a normal voltage of 13.9-14.2 the headlights ran normally, and now the voltage has been back to the same figures and the headlight issues still persists. i guess the lower running voltage was just there until the BCM/ECM re-calibrated to the new ground

at this point we are thinking the problem could be a failed current sensor not relaying the right load back to the BCM which is calling for a higher voltage, but would this cause the headlights to flicker? the current sensor only comes with the negative battery harness and to completely replace the harness is not an easy job on these trucks, looks like the fuse box in the engine bay has to come out and the negative that mounts to the block sits above the front differential and is a pain to get to.

anyone here have any thoughts or opinions/ recommendations to check? has anyone seen such a thing?

The problem is with the crap aftermarket LED headlight bulbs, not your GMC.

 

[tcp71]

The problem is with the crap aftermarket LED headlight bulbs, not your GMC.

With poorly designed housings that really just blind other drivers without actual headlight improvement. These days the world is full of that cr@p.

 

[Thermo1223]

With poorly designed housings that really just blind other drivers without actual headlight improvement. These days the world is full of that cr@p.

Luckily my projectors are pretty decent otherwise I'd stick with halogens. I also adjusted the aim.

 

[Jetronic]

pretty sure the headlights should get a constant voltage There should be a device somewhere that keeps the voltage constant for sensitive devices.

 

[_LeO_]

What is the "new" alternator? Is it a rebuilt or new? What brand is it?

Modern vehicles usually have some sort of charging management software. Where? So the manufacturer can eeeek out an additional 0.05mpg. Basically, the software stops the alternator from charging under certain conditions. Those conditions vary by manufacturer. I would also check grounds, especially the engine to chassis ground cable.

they are re-manufactured, the second one was an OEM.

we ran a new ground from the alternator to the battery terminal already, this corrected the issue for a day or so.

The problem is with the crap aftermarket LED headlight bulbs, not your GMC.

i've had the crap LED headlights for 4 years, never an issue. its not the headlights as everything was functioning fine 3 months ago. and these aftermarket headlight bulbs are anything but cheap and crap. Morimoto makes some of the best bulbs out there. so please if you don't have any helpful suggestions on how to approach the issue i'm having move along and save us both the time

 

[_LeO_]

pretty sure the headlights should get a constant voltage There should be a device somewhere that keeps the voltage constant for sensitive devices.

there likely is, i've tested the voltage to the socket and when the battery is reading 15volts the sockets are 13.7xxx volts, there's minor variances but not enough to cause the driver of the LED to cause the diode to flicker.


looking at the Body builder manual for my truck it looks like the headlights come directly off the BCM so i'd assume the BCM is regulating current and voltage to the actual bulb.

as mentioned every time the brakes are hit or even when i turn on my signals and the system is loaded up a bit more, the flickering and dimming happens, which is why both my mechanic and i are thinking it has something to do with the current sensor and why i initially though it was the battery/alternator. also looking at the charge system modes, the only time i should be at 14.5 volts is when the truck is first started and its being charged fully. else it should be around 13.9 volts

 

[kschachn]

i've had the crap LED headlights for 4 years, never an issue. its not the headlights as everything was functioning fine 3 months ago. and these aftermarket headlight bulbs are anything but cheap and crap. Morimoto makes some of the best bulbs out there. so please if you don't have any helpful suggestions on how to approach the issue i'm having move along and save us both the time

Odd you're having an issue then.

 

[Thermo1223]

Have you check and cleaned every engine bay ground? Checking the wires for splits and corrosion?

 

[_LeO_]

Have you check and cleaned every engine bay ground? Checking the wires for splits and corrosion?

the ones i can see look clean, problem is theres a main battery ground on the boy under the fuse box that is a chore to get to. if anyone knows a ohm reading that i could potentially use to test the grounds, as of right now all grounding gets continuity to the negative battery terminal

 

[Thermo1223]

the ones i can see look clean, problem is theres a main battery ground on the boy under the fuse box that is a chore to get to. if anyone knows a ohm reading that i could potentially use to test the grounds, as of right now all grounding gets continuity to the negative battery terminal

Looking and actually taking them apart to clean them are two different things. I'd clean every last one of them as well as test the current sensor.

 

[Opelman]

I'd look at the body to chassis/ engine ground.

 

[wag123]

i'd assume the BCM is regulating current and voltage to the actual bulb.

The voltage going to the headlamps is not regulated, the voltage regulation is being done inside the bulbs themselves (typically PWM voltage regulation in LEDs), this is why I called the aftermarket bulbs crap. How much you pay for the bulbs doesn't automatically make them not crap.
Something that you might want to check is the amount of A/C ripple voltage in the DC when the engine is running. It shouldn’t exceed .05V. High ripple voltage can/will wreak havoc with PWM regulation circuits. Excessive ripple can be filtered-out by putting an electrolytic capacitor on the positive power leads of each LED as close as possible to the LEDs themselves, 4700 mfd 35v capacitors should do the trick.