Trailer brakes not working

[Dave27]

Your 7 way plug is replaceable on the truck. Disconnect this from the truck bumper and disconnect from the vehicle harness. You can then check the connections at the harness where it pugs into the 7 way plug just behind the bumper.

Check for diagnostic codes for the brake controller.

This can all be done at the dealer and while they should find the problem quickly, their hourly rate can be high.

One thing that is important on GM trucks. You will want to use only a Pollak plug.

Pollak Replacement 7-Pole, RV-Style Trailer Connector Socket - Vehicle End Pollak Wiring PK11893

Jim

I had a receiver installed in the side of the truck bed when the hitch was installed. I checked both this one and the one in the bumper. There was not power to the brake pin when the brake controller was activated in either of them. While we were traveling I would switch between the two receivers and there was no difference. I checked for diagnostic codes and there weren't any on the truck.

Dave

[Guest]

Dave,

If someone has added in a harness and plug in the bed, for the fifth wheel, you may want to check where they tapped in to add in this plug. If its a direct plug in, it may be good to check those connections.

Jim

[Cate&Rob]

Is there any chance that the trailer brake circuit is disabled because the truck is not moving?

Rob

[Jkwilson]

A tip that can help find a loose wire is to get a portable AM radio. Tune it to a space between stations. Hold it in your hand while wiggling wires that are or should be powered. When moved, loose connections will make a very notable crackling in the radio.

[ncitro]

Is there any chance that the trailer brake circuit is disabled because the truck is not moving?

Rob

I have no experience with GM but I know this can be a thing on Ford. The computer will sometimes not engage the trailer brakes if the vehicle is not moving or if it does not detect the trailer brakes.

I would take it to the dealer, they've got a magic box the plug into the 7 pin that mimics a trailer and let's them test everything. With all the software in the vehicles these days I think even though they're expensive a dealer is your best bet for diagnostics.

Another option before that would be to hook it up to another trailer if you know somebody with one. See if it's got the same issue (tough with intermittent problems I know).

[Guest]

I'm not aware of GM using a minimum vehicle speed to operate the trailer brakes. But It would be best to use the brake slider to check for voltage anyway, and if this works but activation does not work with the pedal, it may be worth checking the brake pedal position sensor. This is different than the brake light function, but they may be integrated. I measure those signals at work but have not replaced a sensor. I have a MY15 truck and will take a look tomorrow to see if there is a single or dual sensor installed.

Not pushing the dealer option but brake pedal position could easily be checked with a GM or other high end generic scan tool.

A diagnostic fee is typically $100 from a dealer where a small shop or auto parts store with a quality scan tool can plug in and check it.

Jim

[ncitro]

I'm not aware of GM using a minimum vehicle speed to operate the trailer brakes. But It would be best to use the brake slider to check for voltage anyway, and if this works but activation does not work with the pedal, it may be worth checking the brake pedal position sensor. This is different than the brake light function, but they may be integrated. I measure those signals at work but have not replaced a sensor. I have a MY15 truck and will take a look tomorrow to see if there is a single or dual sensor installed.

Not pushing the dealer option but brake pedal position could easily be checked with a GM or other high end generic scan tool.

A diagnostic fee is typically $100 from a dealer where a small shop or auto parts store with a quality scan tool can plug in and check it.

Jim

I've never used one but I do know things like this are available for testing the truck:

Innovative Products Of America - 9107A Electric Brake Force Meter w/Dynamic Load Simulation and Circuit Testing Black https://www.amazon.com/dp/B073FJ5NVL..._rU7-FbV73W3ME

Or

CURT 51498 7-Way RV Blade Trailer Brake Controller Tester https://www.amazon.com/dp/B00NUFW500..._tV7-FbEVNP417

But for the cost it's probably cheaper to have it looked at. Unless you like having tools and test equipment which is certainly possible and fine lol.

[Country Campers]

I agree with Neil ncitro . Hook your truck up to another trailer and also have someone else hook your trailer up to their truck. Use the slider to try the brakes on both accounts. You may also try to put the truck in gear and see if that changes any of your finds.

Brian

[Cate&Rob]

This does not explain why pulling the break-away pin does not energize the trailer brake system. This may be an unrelated parallel failure. I would suggest bypassing this switch with a jumper wire (can be done at the pin box trailer battery to brake apply terminals) to confirm that the trailer brakes do work.

Rob

[Dave27]

I went to a Chevy dealer this morning, had a good talk with the service rep and he referred me to an RV repair place that has more experience with this than the dealership does. The dealer will want the truck all day, and they are booked for a while. The RV service guy was very helpful and attached a devise that simulates a trailer. The truck checks out fine. Since the problem is intermittent, it doesn't eliminate the truck, but I going back to the trailer. The brake controller is "smart" which can explain why it responds based on what it "thinks" is going on
thank you everyone for you suggestions.
Dave

[Dave27]

Dave27
I would agree with Neil's analysis. The first splice (that will affect all four brakes) is at the left front wheel. On the feed side from the pinbox, check the colored wire for +12V when brakes are applied. Check the white (or maybe black) wire for continuity to ground.

BTW, the non-functioning break-away apply could be a a separate problem. These switches fail open if the pin is not pulled and the contacts lubricated on a regular basis.

Rob

Cate&Rob ncitro Yoda Guest TucsonJim

Look at what I found! The brake wires coming into the first split are protected by a cover. It looks like the wires rubbed together where they go through the coroplast (at least I can't see any other explanation). Note there is bare wire on both, and the wire covering on one looks like it started to melt or burn. Where do I get water proof splitters? Are these the best, or should I use something else? How do I protect the wires passing through the coroplast? Just tape them?

At this point I plan to replace these two wires and since they are such an obvious problem stop there and see how things work. If there are still problems, I will go further. Maybe when I'm back home I will look at rewiring the brakes from here.

Thank you so much for the guidance. If you can point me in the right direction for the splitters, I would appreciate it.
Dave

[TucsonJim]

Wow, that sure may be the problem with your brake malfunction. I'd certainly tape it up for a temporary repair. Here is a link to the connectors - They are a little pricey, but I like using them.

https://www.amazon.com/3M-Scotchlok-...xpY2s9dHJ1ZQ==

[Dave27]

Wow, that sure may be the problem with your brake malfunction. I'd certainly tape it up for a temporary repair. Here is a link to the connectors - They are a little pricey, but I like using them.

https://www.amazon.com/3M-Scotchlok-...xpY2s9dHJ1ZQ==

I'm not reusing this wire, it's even worse than it looks in the photo. Part of the wire was laying under a thicker one, it wore through to bare wire and started to burn the thicker wire cover above it! The jumble of wires laying against each other in the underbelly seem to have contributed to this problem. These look like they are only 16 gauge, that seems very small for such an important application that must draw a fair amount of current. The blue wire it is split from looks like it might be 12 gauge, would it make sense to use 12 or at least 14 to replace the 16, or would there be an unintended consequence? It looks like the wire going into the brake drum is only 16 too.
Dave

[TucsonJim]

I'm not reusing this wire, it's even worse than it looks in the photo. Part of the wire was laying under a thicker one, it wore through to bare wire and started to burn the thicker wire cover above it! The jumble of wires laying against each other in the underbelly seem to have contributed to this problem. These look like they are only 16 gauge, that seems very small for such an important application that must draw a fair amount of current. The blue wire it is split from looks like it might be 12 gauge, would it make sense to use 12 or at least 14 to replace the 16, or would there be an unintended consequence? It looks like the wire going into the brake drum is only 16 too.
Dave

No problem. You can certainly replace that wire with a larger size.

Jim

[ncitro]

Dave27 Glad you found the cause! I've had good luck with the heat shrink butt splices, but it's tricky with multiple wires coming together. I'd go with what Jim linked, or if you're skilled you could solder, heat shrink and then coat it with liquid electrical tape. For the penetration, maybe a thicker wire like meant for direct burial? Otherwise maybe some silicone in the hole where it goes through to hold it in place and keep it from vibrating? It shouldn't need to move or flex above the coroplast as long as you leave enough below it.