Community Forums

e.menoche · 01-30-2023, 09:25 PM

Hey gang! I find myself in a bit of a pickle. While towing, my truck is intermittently reporting "check trailer wiring," then quickly, "trailer connected." In-between, I have no trailer brakes! This was happening every one to two minutes.

I took the truck to the local GMC dealership and explained the problem. They cleared some error codes, replaced a switch, attached the truck to a towing simulator, and procikmed that all was good.

Took the trailer out and all was not good. Problem recurred before moving 50 yards.

I had a rv tech check out the trailer wiring. He found a disconnected wire at one of the brakes (!!!) and replaced the umbilical cord, and proclaimed all was good.
I also pulled the emergency separation pin, and the brakes locked as they should. So.seems like the trailer checks out. Yes?

Took the trailer out, and all was still not good. Nothing has changed for the start. See first paragraph.

So what do I do now, to avoid being caught in the middle with the truck folks pointing to the trailer, and the rv folks pointing to the truck (which I think is the correct answer)?

I'm taking the truck back to GMC tomorrow for further diagnosis, and probably more $$$.

code2e · 01-30-2023, 11:40 PM

Sounds like an intermittent poor connection at your trailer connector. If you live in an area with road salt usage or near the ocean, corrosion can be a problem.

Manual cleaning or chemical cleaning may be your answer. I attached a picture of the best electric cleaner I know of, DeOxit. Just spray in the the connector body and the pigtail terminals. It air dries.

To manually clean you need to disconnect the battery negative cables. There may be hot terminals due to battery charging circuit. Then clean the surface of each terminal with a small wire brush or scrape with a small knife blade.

I have recommended the DeOxit to several fols and always gotten good feedback. By far the easiest way. Good for shore power connections as well. Good luck.

carybosse · 01-31-2023, 06:49 AM

There have been issues of bad connection of wire harness to the 4/7 pin connector on the truck, back under the bumper.

It would be great if you could get another GM truck to tow your trailer to check it out and for you to use your truck to tow a different trailer with trailer brakes.

EDIT:
Unplugging and re-plugging the various connectors on the wire harness can "fix" the problem, but using something like code2e suggested is a good idea as well.

Most modern electrical connectors are designed that when you plug in the connector, the action of the male and female terminals mating, in a very non-sexy manner, should scrape the corrosion off and create a good electrical connection.

mistercee · 01-31-2023, 08:24 AM

Did the RV tech pull the wheels and hubs off the trailer and check the brake wiring there?

I had a wire pull out of one of the retaining clips and over time it rubbed the insulation away in a spot, causing intermittent shorts. This issue caused the same 'trailer disconnect' message and random brake/no brake scenarios you are experiencing.

e.menoche · 01-31-2023, 01:29 PM

Quote:

Originally Posted by mistercee

Did the RV tech pull the wheels and hubs off the trailer and check the brake wiring there?

I had a wire pull out of one of the retaining clips and over time it rubbed the insulation away in a spot, causing intermittent shorts. This issue caused the same 'trailer disconnect' message and random brake/no brake scenarios you are experiencing.

No, he did not. That could be a fruitful path of inquiry. I will ask him about it.

e.menoche · 01-31-2023, 01:47 PM

Quote:

Originally Posted by code2e

Sounds like an intermittent poor connection at your trailer connector. If you live in an area with road salt usage or near the ocean, corrosion can be a problem.

Manual cleaning or chemical cleaning may be your answer. I attached a picture of the best electric cleaner I know of, DeOxit. Just spray in the the connector body and the pigtail terminals. It air dries.

To manually clean you need to disconnect the battery negative cables. There may be hot terminals due to battery charging circuit. Then clean the surface of each terminal with a small wire brush or scrape with a small knife blade.

I have recommended the DeOxit to several fols and always gotten good feedback. By far the easiest way. Good for shore power connections as well. Good luck.

I used that for the first time ever a couple of weeks before the problem started. Coincidence? Thought I was doing the right thing.

0rion · 01-31-2023, 02:20 PM

I'm guessing no one you know has a trailer to hook to and see if the problem follows the truck? That would quickly point you in a direction.

carybosse · 01-31-2023, 02:43 PM

Quote:

Originally Posted by e.menoche

I used that for the first time ever a couple of weeks before the problem started. Coincidence? Thought I was doing the right thing.

I would probably use that cleaner, but then apply a bit of dielectric grease before snapping the connectors back together.

You may have cleaned the existing dielectric grease out and allowed dirt to get in. Or, you may have just caused a problem that was going to rear it's ugly head eventually to show up earlier.

(There may be no "right" thing with modern electronics. )

e.menoche · 01-31-2023, 10:00 PM

Quote:

Originally Posted by carybosse

There have been issues of bad connection of wire harness to the 4/7 pin connector on the truck, back under the bumper.

It would be great if you could get another GM truck to tow your trailer to check it out and for you to use your truck to tow a different trailer with trailer brakes.

EDIT:
Unplugging and re-plugging the various connectors on the wire harness can "fix" the problem, but using something like code2e suggested is a good idea as well.

Most modern electrical connectors are designed that when you plug in the connector, the action of the male and female terminals mating, in a very non-sexy manner, should scrape the corrosion off and create a good electrical connection.

Actually, the guy next door has a GMC towing a Montana. Wonder if he’d be willing to try that experiment.

Nwcid · 02-01-2023, 08:32 AM

My 2016 Chevy does that occasionally with my car trailer. I dont recall it ever happening with my 5th wheel.

Typically it is a dirty or loose connector (this trailer get abused). Once I get in and clean and/or adjust the contacts the problem goes away.

Is there a common time that this happens like after making a turn or big bumps? If so that is likely to indicate a poor connection, either at the main connection or somewhere along the way.

tpaul · 02-03-2023, 07:24 PM

Do you have an integrated trailer brake control in your GM vehicle. These are very sensitive to changes in the grounding. Not just loss of ground due to a bad connection but also if an alternative ground path develops. This happened when the paint on our weight distribution bars wore off and the system was sensing an alternate ground path through the hitch. Solved when I put the pads back on the L bracket holding the bars (the pads are designed to reduce squeal but they also serve to insulate the bars from the L bracket). Prior to this I had done about everything else to no avail. Replaced the plug. Cleaned all connections. Etc.