No power to trailer lights

Arthur87 · May 5, 2020

Yes, I just bought a 2020 Sierra SLT. When I hook up the trailer and connect the 7-pin adapter to 4 blade wiring harness, no lights, and the Infotainment System shows "No Trailer Detected". Of course, the dealership is completely oblivious of this and want me to bring the truck in to the service department. This should not be the procedure. That is a waste of my time. A little background on this situation, I just bought a boat and thought maybe it was the trailer lights or the wiring harness but none of the lights work on the trailer once hooked up to the truck. So I hooked up my 2001 Tahoe to the boat trailer and all the lights work.

Christop · May 11, 2020

driving 2020 silverado z71 bought in december

today wanted to put jet ski in water hook up trailer only getting right turn signal

no left turn, no running lights , no break lights or hazards

so me i change all 2 1157 bulbs on trailer only right turn signal

plugged into 4 pin directly to vehicle connection

then tried the optional round connector to flat 4 and flat 5 connector get right turn only.

hooked up trailer to friends vehicle everything works

tested with volt meter

power to green right turn only nothing on other wires

changed all trailer fuses in fuse box still nothing

from what i read guessing i will be dropping jet ski in water with right turn signal only until i can get it to dealer

i had the same issue with 2017 silverado it was the harness

GMCustomerService · May 15, 2020

Hi, all. This is certainly not the sentiment we wish to see. Our team would like the opportunity to research these concerns on our end. In order to get started, please send an email to [email protected] ATTN: forum username/ GM Trucks with your contact information, VIN, brief description of your concern, and preferred dealership. We look forward to hearing from you. To learn more about GM's privacy policy, please visit http://bit.ly/2h3ZUnC.

Aleigha W.

Marc L · May 19, 2020

I had the same problem this past weekend on my 2020 Sierra 1500 AT4 (with less than 5,000 miles on it). Hooked the boat trailer up to the wife's SUV, and everything worked great. It was a real bummer that I have a brand new truck that couldn't pull a trailer. I hope the dealership can resolve this issue (my appointment is next Monday). As much as I like this truck, I don't have much use for a truck that can't pull a trailer.

Edited May 19, 2020 by Marc L

jeff osborne · May 19, 2020

It's really a shame. I've been a GMC guy all my life and now to be tested like this is pretty low. I don't know whom to blame more, AutoNation it GMC. I bought it new in December and it's been in the shop more than 79 days! I think the worst thing is that while going through the work orders, I found out that my truck was in an accident and had the front fender replaced! AutoNation didn't bother to disclose that. I found out when I thought about trading it back in on a new one and the sales manager asked me how bad the wreck was. I would never have bought as new truck that had been wrecked. He then told me my truck was worth substantially less because it had been wrecked. I asked that the AutoNation general manager could please call me because I wanted to mitigate this problem locally, just between us guys. Still no call, still in the shop. GMC engineers think they may have fixed the electronic gremlins but that doesn't help the fact that it's been in an accident. I'm not sure what I'm going to do next but this is not over. Good luck with yours! I see that there is a service bulletin it on the trailer wiring controller. Could be your issue.

Marc L · May 21, 2020

Thanks. That's a shame about your situation, I have to believe that GMC Corporate would step in and not only penalize the dealership, but somehow make the situation right for you. I can imagine how hard it is, but try not to let the one bad apple (Auto Nation) spoil the bunch (GMC) for you.

I'll post up with the resolution to my situation is (I'm assuming they'll be able to fix it without keeping the truck for 70+ days).

JohnMr19 · May 26, 2020

I had similar problems with my 2019 Silverado Trail Boss. I move every year for my job and pull a cargo trailer to do so. Before I bought my new truck, I pulled the trailer with my 2015 Silverado LT and never had any issues. After trading vehicles last fall, I hooked up my trailer to the new truck and discovered none of the running lights would work and I would quickly get the "trailer disconnected" message (when the truck would actually detect the trailer). The electric brakes didn't appear to work either. Running the light check (Advanced Trailering Package), I found the brake lights and turn signals (LED) worked but not the running lights (incandescent). I also get a trouble message showing which pin was not working on the connector when the light check would fail.

Assuming the trailer was not the issue since I had pulled it earlier that year without any problems (and the error message), I made a service appointment to have it checked out. I had already made sure the wiring harness was connected to the back of the 7-pin connector and all the fuses were good. The dealership said a couple of the pins on the connector had "high resistance" and replaced the connector. Thinking my problem was solved, I hooked up my trailer and found that while the "trailer disconnected" issue seemed to be solved now, the running lights still didn't work - they would come on for about a second and then go off. I bought a 7-pin connector tester and everything works correctly - maybe there's an issue with the trailer after all?

We have a cargo trailer at work, so I hooked it up to my truck and everything works fine. The truck detected the trailer right away, so I created another trailer profile and ran the light check - all good. Doing some research online, it sounded like a bad ground could be causing the running light issue. Checking each light, I would disconnect one light at a time and try the lights. I found the running lights would stay on when I had the passenger side/rear/upper disconnected. It also looked like the socket for the plug-in light had some corrosion, so I cleaned it up with a wire brush. It would still cause the lights to go out after about a second once the light was reinstalled, so I bought a couple of new plug-in lights and replaced it - viola! Feeling pretty proud of myself, I packed everything up and prepared to leave the storage lot where I keep my trailer. One last check before I go: Lights go off after a second - son of a b**tch!

Research online also mentioned possibly drawing too much amperage with incandescent lights, so I bought five plug-in LED lights and swapped them out with five old lights - works like a champ! I made the move this winter and never had any more issues. I did notice one night while staying at a hotel, the trailer brake lights would periodically flash dimly when the truck was turned off and locked. I discovered in another thread that is a security feature that causes the alarm to go off if someone disconnects the trailer - cool! I've been thinking about replacing all the incandescent running lights with LEDs, but reading this thread it sounded like it might cause another issue if there's not enough amperage being drawn. Maybe I'll quit while I'm ahead.

Marc L · May 26, 2020

JohnMr19 - But why on God's green Earth would GM make it so their trucks could only pull trailers equipped with LED lighting systems??? There has to be a problem with the system somewhere; I cannot imagine that GM would purposely engineer their trucks this way. Additionally, there are TONS of trailers still running around with incandescent bulbs on them that are being pulled by these trucks without issue.

My dealership originally told me it was a problem with my trailer wiring because their test set didn't detect any problems with the truck. This was a total garbage answer, so I asked if I could bring in my boat trailer to try and see if another 2020 Sierra would recognize it. This truck did not give the same "trailer not connected" error that my truck displays. This truck apparently registered there was a trailer because it went through a series of tests for the trailer's lights. Unfortunately, we were not familiar enough with the trailering app to get past this point. At least we know that another vehicle recognized my trailer and the problem is not with the trailer's wiring, as originally thought by the service department. The Service Manager said that he would be reaching out to GM today to see if they had any ideas on the problem. I also emailed GM Customer Service about the issue. I am eager waiting a response on the issue.

I bought a truck with the intent to tow a boat, and possibly a camper as well. As of right now, I have a $65K vehicle that was supposedly built to tow, but is incapable of doing so. I have no use for this truck if it cannot even tow a trailer.

Edited May 26, 2020 by Marc L

JohnMr19 · May 27, 2020

Marc L - I'm still not 100% sure if the issue lies with the truck or my trailer. The dealership did find the 7-pin connector bad and replace it before I began to troubleshoot the trailer. It's possible there could be more than one issue on the trailer drawing too much amperage. Replacing some of the old lights with LEDs may have lowered the total amperage enough to bring it within tolerance. I know that's a stretch, but remember when I connected my truck to a different trailer (after the 7-pin connector was replaced), everything worked fine. I have to assume my trailer was at least partly at fault.

I know this doesn't really help everyone else who is experiencing this problem, but I wanted to share my experience. I agree with you that this whole situation is unacceptable and GM needs to figure it out and correct it. I remember the first time I connected my trailer to my new truck, I thought the whole 7-pin connector mounting felt pretty flimsy. Turns out the connector was bad - maybe there's a lot of bad connectors out there. Have you checked your connector with a tester?

jeff osborne · May 27, 2020

I bought an led lights strip for the rear of the truck when brand new.i plugged it in and every light went to the left blinker. I unplugged it and never used it again since my trailer light tested shows failure. The local GMC pointed at the led strip and fixated on it as the culprit for months even though it's not connected. I finally got upset with their tunnel vision and literally ripped off the lights and through them in the trash in front of them. I said now what's wing with it? They're answer was*nothing wrong with it*. But trailer lights still not working so something must be won't. They just shrugged and walked away. GMC engineers asked me to bring it back 2 days later because there is obviously still major electronic issues. Still no luck with buy back or lemon law but getting close to an answer I think. I'm betting I won't like the answer but I think I'll get one soon.

Mogur · May 27, 2020

I bought a 2020 LT with 3.0 Duramax. I thought the price was low, so I jumped on it. Since it is a double cab, this configuration is pretty hard to find.

It was 300 miles away in another state. When I got to dealership, they said it was a "loaner" and had 1000 miles on it. They gave it out to people who had their own vehicle "captured and laid away for service".

In general, it looked good, and highest mpg was 45, average 34, so I thought it had not been driven hard. I admit they gave me what I wanted for trade-in value. I needed a truck to pull a trailer. Whatever.

I will hook up my cargo trailer and hope for the best. I am marking this thread so I can find it again.

cheers, from near Yellowstone NP.

YMMV

Mogur · May 27, 2020

A POSITIVE COMMENT AND PRAISE FOR CHEVROLET & GM!

HooRaaaay! My 2020 Silverado w/3.0 Duramax is utterly fantastic! I connected trailer and all the lights, turn signals, brake lights, Trailer Brake settings and all WORK FINE!!! The truck "sees" everything, and no problems.

I know the trailer weighs 4200# empty. I have converted a 7'X14' cargo trailer to toy-hauler (ATV, Ural Motorcycle, std motorcycles, bikes, 12' Fold-Up Flat Boat-FOLBOAT)+ camper with the usual stove, sink, small toilet-shower room, fold-up (like Murphy) bed, TV, cabinets, and shelves. The heaviest motorcycle is 788#. I didn't put any of the "toys" inside, but I went for a test-spin in my area.

I live in foothills, so immediate left up the connecting street goes up 500' and a 2 mile circle. The 3.0 Duramax did not even notice the weight, simply amazing! Power is awesome! Sure it makes more noise/sounds and mpgs dropped to 14, but that was all hills. I expect it will be better on a long haul to fishing/camping areas via some highway speeds. Almost zero noticiable sag in the back end trailer hitch, I need to adjust the tow/receiver thing up/down to correct for a level trailer.

I had a 2018 Colorado 2.8 Duramax. It was/is an excellent truck in my opinion. Three problems, 1) no tow mirrors available for it, 2)could not see around the sides of trailer, 3) a "short-bed" is too damn short, and hardly a "bed". Other than that, it did fine, but I admit that hauling the toy-camp trailer was a lot of effort, do-able, but really not comfortable for me. So last month I traded for Silverado Double-Cab, Duramax, which gets me almost the same length, but a longer "bed". The Silverado is bigger and does the same job A LOT better. Works for me.

Forums have so many complaints and problems that I was Very worried I would have computer/re-flash/electrical problems. So far, no goofy electrics and rear solid window does not leak. It snowed 6" here on Sunday 24th, the next day was 68F. Truck did not care about the snow did justfine up my 200 yard driveway hill.

If anyone has suggestions on what to choose "gain" for trailer brakes, I would appreciate suggestions. Thanks in advance. It is nice to know that Chevrolet DOES build a good product, at least I chose a good one. Thankful, amen.

YMMV

Edited May 27, 2020 by Mogur

davester · May 27, 2020

What to use for the gain depends on the specific trailer brake controller, the trailer brakes, how heavy the trailer is (so, higher gain if trailer is loaded).

AJMBLAZER · May 27, 2020

With my trailer I had to dial the gain WAY back to 1.5%. Works fine now.

Marc L · May 29, 2020

Update - Issue resolved.

I was sure the problem wasn’t with my trailer since it connected to two other 2020 Sierras. I decided to connect my truck to multiple various trailers (seven and four pin), and my truck registered the connections to all of them. After that, I decided to take a look at my trailer wiring. I needed to find a resolution to the problem! There was some corrosion in the ground for the trailer. I cleaned it up real good and put everything back together, and BOOM! The truck registered the connection!

Not sure why the corrosion was enough to prevent my truck from connecting with the trailer and not enough to cause an issue with the other trucks. Maybe the sensors or computer on mine is more sensitive? Regardless, it is fixed and I’m happy.

Edited May 29, 2020 by Marc L