Trailer Brake Issue

marpel · October 1, 2022

'22 Sierra 2500 HD.

Actually a couple questions.

After a complete overhaul (new wiring/new brake assembly/new junction box/new 7 pin cable/ensured proper connections and ground and star wheeled the correct drag etc) of trailer brake system, I pulled the trailer to set the gain in anticipation of trip. At that time, using the OEM brake controller resulted in absolutely no trailer brakes. Took the truck into the dealer who confirmed an issue and kept the truck for 2 days only to advise it was fixed and the issue was a loose fuse somewhere not even directly related to the brake wiring. But I was assured everything worked OK.

Believing the system was working, hitched up the trailer the day before we were to leave and a test run proved the system was not working and had to push gain to 10 to get a moderate tug on the brakes (using brake controller by hand), but no lock-up (with the previous truck, 2012 Sierra and same trailer, I was able to easily lock the brakes), but pretty poor performance with using brake pedal. Because we were committed to leave, I pulled the trailer to/from Vancouver BC and Denver Co, and had to manually use the brake controller for slowing/stopping. A lot of anticipating slowing/stopping, and a big pain but doable.

As I am an electrical newbie, I don't know for sure, but it seemed as if the foot brake was not providing enough voltage to the system, and working the brake controller by hand was a bit more powerful, but still not peak voltage.

Plan on returning to dealer.

But to prepare myself, is the above possible, where a connection issue at the foot brake, and less so at the brake controller, causes a lack of voltage to the system, resulting in a reduced application of the brake at the wheel? And if this is true, is there a device that can be hooked to the truck's 7 pin to conclusively determine the voltage output? If this is not so, any info that I can use in my conversations with the service rep. When I first took the truck in and they "fixed" the problem, I was unaware enough to just believe what they told me. But I would like to be better prepared this time.

And a couple of unrelated questions:

Is driving in L6 the same as driving in D (6th gear)? In other words, is there any issue with driving in L6?

And why, when the truck is in D (in 6th gear), and putting it into L, does it drop down two gears into L4? The same happens when in D (5th) and put it in L, it drops two gears down into L3? To me, logic suggests it should go from D(6) to L6 and similarly from D(5) to L5. This is on flat grade with no load.

Sorry for the long post,

Marv

asilverblazer · October 3, 2022

On 9/30/2022 at 11:14 PM, marpel said:

...I pulled the trailer to set the gain in anticipation of trip. At that time, using the OEM brake controller resulted in absolutely no trailer brakes...

...the system was not working and had to push gain to 10 to get a moderate tug on the brakes (using brake controller by hand), but no lock-up (with the previous truck, 2012 Sierra and same trailer, I was able to easily lock the brakes)...

...is the above possible, where a connection issue at the foot brake, and less so at the brake controller, causes a lack of voltage to the system, resulting in a reduced application of the brake at the wheel? And if this is true, is there a device that can be hooked to the truck's 7 pin to conclusively determine the voltage output...

...Is driving in L6 the same as driving in D (6th gear)? In other words, is there any issue with driving in L6?

And why, when the truck is in D (in 6th gear), and putting it into L, does it drop down two gears into L4? The same happens when in D (5th) and put it in L, it drops two gears down into L3? To me, logic suggests it should go from D(6) to L6 and similarly from D(5) to L5. This is on flat grade with no load...

If you are comparing the built in trailer brake controller to an aftermarket add on controller they won't precisely function the same or result in similar trailer brake action. The built in trailer brake controller isn't inertia based like an aftermarket controller. It will modulate the voltage to the trailer brakes based on braking commanded by the trucks braking system, setting the 'gain' to cause the trailer to lead the trucks brakes or to a level that results in trailer brake lock up may not even be possible.

To determine conclusively that there was "absolutely no trailer brakes" one would need to connect a mulit-meter to the output at the trailer wiring harness and monitor the voltage being applied to the trailer brakes. My normal braking produces a voltage typically less than 3-5 volts but I have seen as high as 7.

Not sure what the exact question of the gear selection is, but I think your description is of normal behavior. Moving the gear lever to a position other than "D" which one might equate to moving it out of over drive in the old days isn't needed in newer trucks, where you instead using the tow-haul function to limit unnecessary shifting and optimize transmission behavior for towing is better.

marpel · October 4, 2022

asilverblazer,

Thanks very much for the response. Likely I did not properly explain my situation/questions.

So, after I reno'd the trailer brake components, I took it for a run and applied the OEM brake controller by hand, but could not get the wheels to lock, even when I put the gain up to 10. I could feel a very mild pull but nowhere close to a lock-up (with old truck and same trailer, I could easily get lock-up even with gain at 6-7).

With the gain at 10, I applied the foot brake and felt nothing. In fact, on the recent trip, when I applied the foot brake, I had to use the brake controller by hand to get any tug by the trailer. I did this for the entire trip. With the old set-up, I had the gain set so when using the foot brake, I could feel a bit of a tug by the trailer, indicating the trailer brakes were contributing to stopping.

I know the trailer side is working as it should, and because I have had the truck in a few months ago for the same issue and after having it for 2 days, they told me it had been a loose fuse and it was fixed. Apparently that is not the case, so I was hoping for information to use when I take it in again for this problem (wondering if they have a diagnostic tool that they could plug in to the 7 pin on the truck which would tell what power the truck is pushing to the trailer when the foot brake is applied.

Regarding the gear questions, as the trailer is only about 5K lbs wet, I found tow/haul to be too aggressive in locations of rolling hills. So I thought, in those locations, I would manually put it into L6 and just shift into L5 during the entire stretch of up/downs, rather than having it automatically jump back and forth between 5 for each uphill and 6 for each downhill. For many of the mild rolling hills, it held pretty good in 6th, but there were a lot of stretches where it would bounce back and forth between D (6th) and D (5th). So I thought I would just leave it in L6 for the most part, rather than D6. But during this manual shift from D6 into L6, I found it did not go straight across from 6th to 6th, but it would drop to L4.

Marv

asilverblazer · October 4, 2022

15 hours ago, marpel said:

...With the gain at 10, I applied the foot brake and felt nothing. In fact, on the recent trip, when I applied the foot brake, I had to use the brake controller by hand to get any tug by the trailer. I did this for the entire trip. With the old set-up, I had the gain set so when using the foot brake, I could feel a bit of a tug by the trailer, indicating the trailer brakes were contributing to stopping...

I know the trailer side is working as it should... I was hoping for information to use when I take it in again for this problem (wondering if they have a diagnostic tool that they could plug in to the 7 pin on the truck which would tell what power the truck is pushing to the trailer when the foot brake is applied.

...in those locations, I would manually put it into L6 and just shift into L5 during the entire stretch of up/downs, rather than having it automatically jump back and forth between 5 for each uphill and 6 for each downhill... But during this manual shift from D6 into L6, I found it did not go straight across from 6th to 6th, but it would drop to L4...

I think you will have a hard time getting an acknowledgement that there is something wrong with the truck, because it is easier for them to blame the trailer.

They could also monitor the trailer brake output using a multimeter, but not sure how they would establish a baseline to compare it to to determine if the truck is indeed at fault. My point being is that it may in fact be sending 'low' or 'insufficient' voltage to the trailer brakes but they could claim it is performing as intended and you would have no way to counter it other than your subjective comparison.

In my opinion, your only course of action that could get some actual results they could work with would be to get them to let you compare your truck to one off the lot. If the one on the lot performs like you expect, monitor its trailer brake outputs and compare it to yours.

I think your transmission is performing correctly, and I agree with your reasoning for the manual shifts too.

marpel · October 5, 2022

asilverblazer,

Thanks for your continued help.

As I have an appointment next week for an oil change, I will speak to the service rep at that time to see what can be done. Although not confident they will give me a loaner for any testing....

Marv

Bob731 · October 7, 2022

I have a 2021 gmc sierra set up with max tow package and i have the same problem with the trailer brakes. Using the foot pedal i can feel the trailer brakes applying a small amount of drag.Using the factory hand controller is the same - small amount of drag. This is a safety factor to me. I would be very interested what the dealer is able to find.

marpel · October 8, 2022

While recently down in Denver I briefly spoke to my D-I-L's brother, who coincidently works in the parts dept of an RV dealership. When he heard my description of the braking issue, he immediately stated that it was a known problem with Chevy trucks (although mine is GMC, I'm sure there is a parallel). However, because he is in parts and not directly involved in the servicing dept, he could provide no specific details.

I have yet been unable to find anyone who "knows" of this problem, and as asilverblazer suggested, if it is truck related, getting the dealer to admit it is uncertain at this point. The last truck I ordered back in 2012, a GMC 6.2, was specifically ordered because it had no AFM as I had previously done a lot of research which showed potential issues with AFM. Funny enough, during conversations with a few dealer employees (sales, others and even managers), everyone expressed no knowledge of any AFM problems. I hope it will not be the same with the braking, if in fact it is a "known" truck issue.

I guess I will find out on Tuesday.

Marv

marpel · October 12, 2022

Bob731,

The (small) difference between our issues is I can barely feel the trailer brakes activate when I press my foot to the brake pedal, but can feel it more (although still unable to make the trailer brakes lock up, by any stretch) when using the hand brake controller. As previously stated, during the last trip, I would apply the foot brake, then have to always use the hand operated brake controller to "boost" the brakes a bit.

Anyway, took the truck in to the dealer for oil change and spoke with the same service rep I had dealt with previously. Informed him of the continuing brake issue, and he connected their device to the truck's 7 pin, which reads and diagnoses things. This time I watched him do it and it appeared to be doing the same thing the truck itself does when a trailer is hooked up and runs through the brake/turn signal protocol. The device indicated no issues. But the rep could not state if the device could identify if the truck was pushing out a (too) low voltage or if it was just indicating the connections were OK and (some) voltage was getting through.

Interestingly, when I told him my previous truck ('12 Sierra 6.2L with tow package) had no issues with the same trailer and I could easily lock the trailer brakes if I wanted (although I had the gain set lower to around 6 for normal driving) he stated I was comparing apples to oranges and the new trucks are set up at the factory so the driver does not notice the trailer brake application and the two work seamlessly together. As I don't know enough about that aspect, I could not dispute his statement. I've dealt with this guy a few times now and he is actually quite on the ball and seemingly sincere.

So, the short version is, nothing was done at the dealership.

As the trailer-pulling season is over for us now, I will have to wait until next season to take another run at this issue.

Marv