GM Towing App Errors

[BryonJ]

We are the proud owners of a 2020 GMC Denali HD 2500 with GM's new towing APP. It's cool, but....

We have been getting two sets of errors:

1 - Trailer Gain not recalled. According to GM this is a software bug within the app and will be fixed at a later date. It does not affect anything other than the app. The ECM (engine control module) still retains the last setting. We see this if we turn off the engine for short periods, such as at a filling station.

2 - Check trailer wiring message (or check brake lights, etc.). We get this error after driving for a while and turning on the turn signal. The truck's turn signal will flash rapidly and the error message will show up in the instrument display. According to GM (see attached) this is caused by either insufficient grounding or a loose connection.

Our local GMC dealer has been great to work with on this. We also learned through them that GM changed their 7-way plug for 2020. The stock Airstream plug was in fact loose, however, we changed ours to match the new GM plug (Pollak) but the problem still persists.

This leads us to the grounding as the cause. Airstream has been of little help. Their response is to blame GM. What GM is telling me is that these new programs are just too sensitive for the way the trailer industry builds their trailers. That said, they are willing to help me troubleshoot the trailer grounding the next time I get the trailer out of storage in August. They did say that other dealers have reported that on some trailers (not brand specific) that they have been finding the culprit in the ground for the electric brakes, especially if exposed to the elements. This past week while camping in GA I was talking to another GMC owner and he had the same problem. They traced his to a faulty rear tail lamp socket on his trailer.

We are towing a 2019 Airstream Classic 33' FB. It does have a lot of lights, so perhaps the grounding is a bit undersized?

I'm curious to hear if other GM owners with the new trailering app have experienced the same problem and whether or not they have been able to resolve it.

[wbrisett]

I did have a bunch of errors with the towing with the 2020 Chevy 2500HD, which was a nothing but trouble, we ended up ditching it and getting the 2020 GMC 2500HD (although we were so close on pulling the trigger on a RAM). I ended up getting a smart tester (https://www.amazon.com/Electric-Dyna...357800-1028535) which is required with new trucks. It was helpful in verifying the problem was not in the Airstream (OK, not entirely true, the connector was a problem, so I replaced it), but in the truck itself.

I would start there. See if your dealer will test the 7 way to ensure it's not on their end. I love the technology on the new trucks, but hate them too because there's so much in the electronics that can go wonky.

[BryonJ]

Originally Posted by wbrisett

I did have a bunch of errors with the towing with the 2020 Chevy 2500HD, which was a nothing but trouble, we ended up ditching it and getting the 2020 GMC 2500HD (although we were so close on pulling the trigger on a RAM). I ended up getting a smart tester (https://www.amazon.com/Electric-Dyna...357800-1028535) which is required with new trucks. It was helpful in verifying the problem was not in the Airstream (OK, not entirely true, the connector was a problem, so I replaced it), but in the truck itself.

I would start there. See if your dealer will test the 7 way to ensure it's not on their end. I love the technology on the new trucks, but hate them too because there's so much in the electronics that can go wonky.

I'm with you on the new technology. Love/Hate

The dealer did test the 7-way. They even installed a device that mimics a trailer. Everything on their end checks out ok. I believe their device is similar to the one you posted.

I will say that the original airstream 7-way did not fit well with the new GM Pollak plug, so we had the airstream dealer make us a pigtail that used a male Pollak plug. The fit is spot on but it did not solve the problem.

[GCinSC2]

ByronJ,

Re: ground concern.

Care to consider rigging a temp/test separate ground wire from truck chassis to trailer chassis?

Gary

[BryonJ]

Originally Posted by GCinSC2

ByronJ,

Re: ground concern.

Care to consider rigging a temp/test separate ground wire from truck chassis to trailer chassis?

Gary

Gary,

Exactly what the attached GM guide suggests. The shop foreman at the dealer is going to help me with that next month as well as some voltage drop tests.

Twin City Buick/GMC in Alocoa, TN is making a loyal customer out of me. Most service centers will not go out of their way to help you like this. They are helping me with the trailer, something they don't sell or service.

Thanks for the suggestion.

Bryon

[GCinSC2]

Bryon,

Sorry I didn't read the TSB that was just a SWAG on my part. Looks like a Pollak 7 way plug by looks and part number too in the TSB. I have the metal housing version Pollak on mine. No issues.

I did run a separate ground on my rig. About 3' or so of common black extension cord SJ. All conductors crimped into one 3/8" ring terminal and other end a 1/4" ring terminal. Shrink wrap tubing etc. Attached to bottom of a tongue jack bolt under coupler and other end to a permanent mounted 1/4" stud I attached to hitch. Star washer and a wing nut to attach. No proof it solved a problem, but it hasn't hurt anything.

Good luck getting this sorted out.

Gary

[driftwood1]

Hmm... I plan to buy a new GMC this fall to tow my 2005 25" Safari.... will follow this thread closely. ByronJ, please keep us updated if you find solution. Wish I could contribute a useful comment to help, but no clue.

[Hermes]

Not that I think that this will solve your problem, but right off the lot, I made sure that the 7-way connectors (male-female) were treated with dialectic grease. There are many corrosion sources out there and this practice has saved us many headaches by preventing contact corrosion. A sealed 7-way cable female plug cover also prevents dirt from entering and crudding up the connector when we are camping or in storage (the TV generally has its own).

[BryonJ]

Originally Posted by Hermes

Not that I think that this will solve your problem, but right off the lot, I made sure that the 7-way connectors (male-female) were treated with dialectic grease. There are many corrosion sources out there and this practice has saved us many headaches by preventing contact corrosion. A sealed 7-way cable female plug cover also prevents dirt from entering and crudding up the connector when we are camping or in storage (the TV generally has its own).

Thanks for your response. A very good practice!

My GMC dealer this for me.

[jaybauman]

I recognize both these problems with my 2020 GMC HD. Empirically, I've fixed them both with 2 small changes to my lashing ceremonies:

1. I use WD-40 (the original stuff) and spray 7-way connectors on both trailer and TV prior to connecting. (The "WD" in the moniker originally referred to "water displacement". My problems first started after camping on the beach, so I tried this and it worked for me.)

2. I don't hook up my 7-way unless my truck is turned off and in "sleep mode" (i.e. green OnStar light is off). I've had less than stellar success when I hook up with the computers live.

While either or neither of these changes may have actually made a real difference, I find I've had no problems since their implementation--and that was 4000 miles ago.

[wbrisett]

Originally Posted by jaybauman

2. I don't hook up my 7-way unless my truck is turned off and in "sleep mode" (i.e. green OnStar light is off). I've had less than stellar success when I hook up with the computers live.

There's still some work to be done in the software I think. the GMC I have seems to be better than the Chevy I had, but then again that vehicle was a total headache which is why after spending more time in the shop than on the road, I threw in the towel on it. But I have noticed that it is better to have the power off when connecting as well.

[kittmaster]

The "check trailer wiring" message was seen on my GMC yukon/trailer also........guess what.....found out one of the trailer brake wires broke on the road....it was telling me there was an issue with the known 4 brakes present down to 3...

Get out there and check to make sure your trailer brake wires are all in tact.

Not kidding, search forum for my trailer brake fix that I had to perform in less than 6 MONTHS of ownership on my brandy new 2019 International Serenity....and that was on the return trip from JC where I mentioned the brake wire loops where larger than I liked.....yeah....let that sink in.