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2020 GM Silverado 3500 HD LTZ
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2 Posts
Discussion Starter · #1 ·
Greetings, How many folks are having problems with their 2020 - 2021 2500 or 3500 trailer towing system? Since I upgraded my 2015 2500 Silverado, I do not have any running or tail lights on 4 of the 5 trailers that I own. It seems the advanced trailer system with integrated trailer towing was released before being fully vetted. I have purchased 3 of the 7 wire to 4 wire adaptors, including one from GM and all have the same results, the brake lights and turn signal work on the 4 wire flat trailers, but no daytime or running light, which makes trip to the early morning boat launch unsafe and illegal. Thus far, all I can get from Chevy is that their trailer system is working fine and my 4 trailers are not compatible with their advanced trailer wiring system; can I please have my dumber system back, that actually worked?? WTH, the 4 trailers worked on my 2015 2500 Silverado and continue to work properly on my wife's 2019 GM SUV. It's ridiculous that GM has not addressed the problem and is blaming our trailers, I would expect more after the purchase of a 77k vehicle. Another annoying feature of the advanced system is a quick flash of the trailer and truck rear lights about every 5 to 6 seconds when the lights are plugged into the truck and it is turned off. It appears that the advanced trailering system is looking for resistive load that the older 4 wire trailers do not have

I am working with GM 2nd tier customer service and will update this post as I get more information.
 

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2021 3500HD GMC Denali
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96 Posts
Yep horrible system. There is no check trailer wiring warning on the dash?


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2021 Silverado 2500HD LTZ L5P
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90 Posts
why not turn on the headlights for those trailers. aluminum frame on the trailer. that can affect ground.

I've never heard of any place requiring daytime running lights for cars much less trailers
 

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Premium Member
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878 Posts
First, go read your owners manual-the flashing lights are part of a security and trailer detection system.
Second, go to gm-techlink.com and search "trailer lighting". Several items there for the new vehicles.
 

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2021 Silverado 2500HD LTZ L5P
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90 Posts
First, go read your owners manual-the flashing lights are part of a security and trailer detection system.
Second, go to gm-techlink.com and search "trailer lighting". Several items there for the new vehicles.
Still dont understand your issue. Are you talking about 4way hazard flashers??

Most states I know of require trailer lights on when headlights come on excluding daytime running lights, turn indicators, brake indicators, and 4 way flash for hazard
 

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2020 GM Silverado 3500 HD LTZ
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2 Posts
Discussion Starter · #6 ·
Update, no help from GM at this point, and it is all 5 trailers, not just the 4 flat wire pin ones, like I initially thought. I like calling customer service and waiting on hold for abut 20 to 35 minutes each time I call, then being told, we will call you back on a given day between x and y o'clock, with no call. The problem is that there are no tail lights on any of my trailers. Recent update, it's all 5 trailers, I assumed it was just the four trailers with the 4 flat wire pin. Tried the 20 ft car hauler with a seven pin plug and brakes this week to go pick up my new tractor, and walah, same problem on that one as well. And again I say, it is a safety issue and illegal, try towing a trailer when its dark down outside down the interstate with no rear trailer lights and a boat blocking the truck lights.

All 5 trailers worked correctly with my 2015 Silverado 2500, and the the 4 flat wire plugs and trailers work on my wife's 2019 GMC SUV. I have purchased 3 different 7 way to 4 way adapters, and none will give me any running or tail lights. The brake lights and turn signals do work. I have a GM case number, but it's doing little good. I hope other GM owners reach out to everyone having this problem. We need to hold Chevy accountable to fix this problem. I also get the trailer and truck lights quick flash about every 5 to 6 seconds as long as a trailer is plugged in (yes, I have heard it's normal, it's the alarm system, but it is not normal for the boat and truck taillights to flash all night if left plugged in) and some annoying trailer is disconnected messages on the message center. I don't think they understand that not admitting and addressing this problem will ensure no Chevy/GM will be considered for future purchases!
 

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1,157 Posts
Im not familiar with the 2020 but just going to ask - are you putting your truck in to tow/haul mode and still experiencing the same issue?
 

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199 Posts
The trailer security system will flash the lights every so often with ignition no matter the type of trailer. Refer to your owner's manual to turn off trailer security. I haven't done it before or I would tell you how.

Is your issue that the running lights do not come on with the vehicle headlights? It sounds like stop and turn function properly.

Are you using a 7 way to 4 way adapter due to having trailer cams connection above the seven way?

#iworkforGM
 

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Premium Member
2020 Chevy 3500 L5P CC LB SRW 2WD LTZ
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34 Posts
I have used the 7 way and all was fine. I did set up the trailer on the infotainment system before checking the lights. Don't know if it worked before that.
 

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878 Posts
Update, no help from GM at this point, and it is all 5 trailers, not just the 4 flat wire pin ones, like I initially thought. I like calling customer service and waiting on hold for abut 20 to 35 minutes each time I call, then being told, we will call you back on a given day between x and y o'clock, with no call. The problem is that there are no tail lights on any of my trailers. Recent update, it's all 5 trailers, I assumed it was just the four trailers with the 4 flat wire pin. Tried the 20 ft car hauler with a seven pin plug and brakes this week to go pick up my new tractor, and walah, same problem on that one as well. And again I say, it is a safety issue and illegal, try towing a trailer when its dark down outside down the interstate with no rear trailer lights and a boat blocking the truck lights.

All 5 trailers worked correctly with my 2015 Silverado 2500, and the the 4 flat wire plugs and trailers work on my wife's 2019 GMC SUV. I have purchased 3 different 7 way to 4 way adapters, and none will give me any running or tail lights. The brake lights and turn signals do work. I have a GM case number, but it's doing little good. I hope other GM owners reach out to everyone having this problem. We need to hold Chevy accountable to fix this problem. I also get the trailer and truck lights quick flash about every 5 to 6 seconds as long as a trailer is plugged in (yes, I have heard it's normal, it's the alarm system, but it is not normal for the boat and truck taillights to flash all night if left plugged in) and some annoying trailer is disconnected messages on the message center. I don't think they understand that not admitting and addressing this problem will ensure no Chevy/GM will be considered for future purchases!
Again, go read the GM Techlink info. It references the exact problem you are experiencing. The tail and park lamps are controlled by a PCB in the control module while the stop and turn are controlled by a different circuit in the module.
The PCB has to see a certain resistance for it to operate the lights- too high or low and it won't work.
By the way, its only illegal if YOU drive it- GM has nothing to do with that- if the truck has a problem they will try to fix it.
 

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3,601 Posts
Do your trailers all have LED or incandescent bulbs? The "new improved" electronics may not play well with whatever bulbs you have....
 

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2021 3500HD GMC Denali
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96 Posts
I recommend taking the truck and a trailer to the dealer to show them there is a issue with your truck. To me it seems you have a wonky module.


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