Trailer Brake Issue

Chadw90 · July 7

Yes it does, but I dont think the controller is working properly. You can have the gain at 10, and manually squeeze it all the way and the brakes hardly drag.
hook up to a different trailer and same thing

Hook up with a Ford and brakes lock up immediately.
I put a 10,000lb skidsteer on a trailer with the Ford and it will skid the tires on the trailer with the gain turned to 10.
With my GMC, you can hardly feel

the brakes drag.

Chadw90 · July 7

The dealer doesnt seem interested enough to investigate any further. They have replaced the 7 pin plug and reprogrammed.

marpel · July 8

Chadw90,

Your recent posts about replacing the OEM controller is interesting. Until now, I did not realize they were available at such a reasonable price. However, is this a component that can be replaced by the owner, or is the job extensive and a shop has to tackle? This would impact the associated cost, of course. If the former, I may take a serious look at that as well.

If you do the replacement, I would appreciate an update.

Marv

BuckWallace · July 8

4 hours ago, marpel said:

Chadw90,

Your recent posts about replacing the OEM controller is interesting. Until now, I did not realize they were available at such a reasonable price. However, is this a component that can be replaced by the owner, or is the job extensive and a shop has to tackle? This would impact the associated cost, of course. If the former, I may take a serious look at that as well.

If you do the replacement, I would appreciate an update.

Marv

I'm pretty sure it's just tucked up under the spare tire and is plug-n-play.

Edit: Never mind, I realize now you're referring to the actual brake controller and not the control module.

Edited July 8 by BuckWallace

newdude · July 9

On 7/7/2024 at 1:21 AM, Chadw90 said:

Yes it does, but I dont think the controller is working properly. You can have the gain at 10, and manually squeeze it all the way and the brakes hardly drag.
hook up to a different trailer and same thing

Hook up with a Ford and brakes lock up immediately.
I put a 10,000lb skidsteer on a trailer with the Ford and it will skid the tires on the trailer with the gain turned to 10.
With my GMC, you can hardly feel

the brakes drag.

The system sets DTCs, so theoretically if there is an issue, the truck would trip a code.

What kind of brake system is on the trailer?

That "control" in the dash is just that, a control. The trailer brake control module is who's behind the operations, the switch on the dash is just an input to the TBCM.

asilverblazer · July 9

On 10/11/2022 at 8:39 PM, marpel said:

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.

I think this will be the most likely answer to trailer brake performance.

Until someone connects a multimeter to measure what output is going to the trailer brakes we'll never know for sure.

GM likes functions to not be noticeable to the driver, like AFM, DFM, traction control, auto 4wd...

marpel · July 10

If the system is designed to work seamlessly and the driver should not notice the application of the brakes, why have a gain control and allow the driver to set it from 0 to 10? And I wonder how the truck would know the condition of the trailer brakes and weight of the trailer, is that not the responsibility of the driver, who in turn sets the gain to ensure adequate brake application by the truck's system?

With my previous truck, I could increase the gain until the trailer brakes locked and slid (around 7 and above). With the current truck, and same trailer, there is no noticeable difference between gain 0 and gain 10.

But you are right, I suppose, without a definite output measurement (which is what I thought the dealership techs should have done), we will never really know.

asilverblazer · July 10

15 hours ago, marpel said:

If the system is designed to work seamlessly and the driver should not notice the application of the brakes, why have a gain control and allow the driver to set it from 0 to 10? And I wonder how the truck would know the condition of the trailer brakes and weight of the trailer, is that not the responsibility of the driver, who in turn sets the gain to ensure adequate brake application by the truck's system?

I don't know... but the truck probably has a sensor that expects an interial change based on the brake pedal application... uses your input on the controller as a 'suggestion' and modulates output to the trailer accordingly.

...goes to see if I can find more concrete information.

asilverblazer · July 10

4 minutes ago, asilverblazer said:

...goes to see if I can find more concrete information.

Enjoy: 2018...

Quote

TRAILER BRAKE CONTROLS

Document ID: 4709945

A trailer brake control system is used to control the amount of trailer braking power that is made available to trailers with brakes that require a controlled electrical output signal for actuation.

The power output to the trailer brakes is based on both the amount of braking being applied by the vehicle’s brake system and on the type of trailer brakes detected.

The Trailer Brake Control System is compatible with two types of Trailer Brake Systems as listed below:

Electric Brakes A controlled electrical output signal energizes an electric-magnet/lever arm assembly that directly actuates the brake mechanism. The GDS name for this system is “Electromagnetic Brakes”.

Electric Over Hydraulic Brakes A controlled electrical output signal energizes a remote, trailer mounted hydraulic pump to build brake pressure in a closed hydraulic system on the trailer. The hydraulic fluid pressure actuates the brake mechanism. The GDS name for this system is “Electrohydraulic Brakes”.

Trailer Brake Output Versus Trailer Brake Type

The trailer brake system characterizes the trailer brakes as either Electric Brake or Electric Over Hydraulic Brake automatically. This characterization may be affected by the number, type, and age of the trailer brake magnets, as well as any other devices installed on the trailer brakes (i.e. adapters for Electric Over Hydraulic brake functionality).

The trailer brake system is fully operational with either characterization.

Some features of the trailer brake system may be different based on the trailer brake type characterization. An example of this is at zero speed, where pressing the service brake pedal will produce output when the trailer brakes are characterized as Electric Brakes, but not when characterized as Electric Over Hydraulic Brakes.

Sliding the manual trailer brake apply lever will produce output at zero speed for either characterization.

The user gain allows the driver to adjust the amount of trailer brake output to match the trailer load and road surface. The controller determines the desired trailer brake output and provides a control signal to the K133 Trailer Brake Power Control Module. The K133 Trailer Brake Power Control Module amplifies the signal and provides the output required to activate the Electric or Electric Over Hydraulic trailer brakes.

The trailer brake control can support up to a maximum of four axles with electric trailer brakes (8 brake magnets).

Connecting a trailer that is not compatible with the trailer brake system may result in reduced or complete loss of trailer braking. There may be an increase in stopping distance or trailer instability which could result in personal injury or damage to the vehicle, trailer or other property. An aftermarket controller may be available for use with trailers with surge or air trailer brake systems.

To determine the type of brakes on your trailer and the availability of controllers, check with your trailer manufacturer or dealer. Do not power up an aftermarket controller with the factory brake controller at the same time.

The vehicle is equipped with the following trailer braking components:

K38A Chassis Control Module-Auxiliary

K133 Trailer Brake Power Control Module

S76 Trailer Brake Control Panel

Manual Trailer Brake Apply

Trailer Gain Adjustment

Trailer Brake Driver Information Center Display

Chassis Control Module-Auxiliary

The K38A Chassis Control Module-Auxiliary is a serviceable GMLAN module. The chassis control module sends the low power commanded duty cycle signal to the trailer brake power control module. The trailer brake power control module amplifies the signal and provides an output that is required to drive the trailer brakes.

Trailer Brake Power Control Module

The K133 Trailer Brake Power Control Module (TBPM) is a solid state power switching module that supplies power to the trailer brakes at the input command duty cycle. Diagnostic messages are sent from the TBPM to the CCM on a dedicated LIN bus.

Trailer Brake Control Panel

The S76 Trailer Brake Control Panel contains the trailer gain and manual apply switches. It is located on the instrument panel to the left of the steering column. Refer to the instrument panel overview for more information on the location. The control panel and switches allows you to adjust the amount of output, referred to as trailer gain, available to the Electric or Electric Over Hydraulic brakes. It also allows you to manually apply the trailer brakes. The trailer brake control panel and switches are used along with the trailer brake display page on the driver information center to adjust and display power output to the trailer brakes.

Manual Trailer Brake Apply

The manual trailer brake apply lever is located on the S76 Trailer Brake Control Panel and is used to apply the trailer’s Electric or Electric Over Hydraulic brakes independent of the vehicle’s brakes. This lever is used in the trailer gain adjustment procedure to properly adjust the power output to the trailer brakes.

Sliding the lever to the left will apply only the trailer brakes. The power output to the trailer is indicated in the trailer brake display page in the Driver Information Center (DIC). If the vehicle’s service brakes are applied while using the manual trailer brake apply lever, the trailer output power will be the greater of the two.

The trailer and the vehicle’s brake lamps will come on when either the vehicle’s braking or manual trailer brakes are applied.

Trailer Gain Adjustment

Trailer gain should be set for a specific trailering condition and must be adjusted any time vehicle loading, trailer loading or road surface conditions change. It is important to re-adjust trailer gain any time the tow vehicle, trailer loading or road surface conditions change or it you notice trailer wheel lock-up at any time while you are towing.

Setting the trailer gain properly is needed for the best trailer stopping performance. A trailer that is over-gained may result in locked trailer brakes. A trailer that is under-gained may result in not enough trailer braking. Both of these conditions may result in poor stopping and stability of the vehicle and trailer.

Trailer Gain Adjustment Procedure

Adjust trailer gain in 0.5 step increments up to 10 gain setting by using the gain adjustment +/− buttons on the trailer brake control panel switch. Pressing and holding a gain button will cause the trailer gain to continuously increment or decrement. To turn the output to the trailer off, set the gain to zero.

Drive the tow vehicle and trailer combination on a level surface representative of the towing condition and free of traffic at approximately 32–40 km/h (20–25 mph) and fully apply the manual trailer brake apply lever mechanism located on the trailer brake control panel switch. Adjusting the trailer gain at slower speeds may result in an incorrect gain setting.

Adjust the trailer gain to just below the threshold of trailer wheel lock-up . Trailer wheel lock-up may not occur if towing a heavily loaded trailer. In this case, adjust the trailer gain to the highest allowable setting for the towing condition.

Hill Start Assist

The hill start assist allows the driver to launch the vehicle without a roll back when the driver is moving their foot from the brake pedal to the accelerator pedal. Refer to the hill start assist system in the anti-lock brake system description and operation document for more information.

Trailer Sway Control

The trailer sway control can detect the vehicle yaw instability, caused by an attached trailer. Refer to the trailer sway control system in the anti-lock brake system description and operation document for more information.

Driver Information Center Indicators and Messages

The following indicators are used to inform the driver of several different conditions:

Trailer Connected

This message will be briefly displayed when a trailer with Electric or Electric Over Hydraulic brakes is first connected to the vehicle. This message will automatically turn off in about ten seconds. The driver can also acknowledge this message before it automatically turns off.

Check Trailer Wiring

This message will be displayed if:

The system detects that a trailer with Electric or Electric Over Hydraulic brakes is connected to the vehicle and then the trailer harness becomes disconnected from the vehicle.

The trailer connection is recognized initially and then a disconnect occurs while the vehicle is stationary. This message will automatically turn off in about thirty seconds. This message will also turn off if the driver acknowledges this message off or if the trailer harness is reconnected.

A disconnect of the trailer wiring harness occurs while the vehicle is moving. The Check Trailer Wiring message will continue until the ignition is turned off. The message will also turn off if the driver acknowledges this message off or it the trailer harness is re-connected or repairs are completed.

There is an electrical fault in the wiring to the electric trailer brakes. The Check Trailer Wiring message will continue as long as there is an electrical fault in the trailer wiring. This message will also turn off if the driver acknowledges this message off.

A poor connection at the 7–way connector may cause the Check Trailer Wiring message. Some aftermarket 7–way trailer side connector adapters or plugs may cause deformation or excessive wear to the vehicle’s trailer terminals. It is recommended that you use an OEM or Pollak heavy duty 7–way trailer side connector adapter.

Service Trailer Brake System

This message will be displayed when there is a problem with the trailer brake control system. The trailer brake system may not be fully functional, or may not be functioning at all. The trailer brake system is designed to provide trailer braking, if possible, even when faults prevent it from being fully functional. This reduced functionality includes:

Providing trailer braking when the master cylinder pressure or brake pedal switch are faulted.

Providing trailer braking when hill start assist and trailer sway control communication is faulted.

Providing trailer braking when certain manual trailer brake apply lever faults are present.

These conditions should be repaired to allow the trailer brake system to be fully functional.

Trailer Gain and Output Display

This display menu can be accessed by scrolling through the DIC menu, or any time the trailer gain +/− button is depressed, or the manual trailer brake apply lever is actuated. The trailer output is displayed from 0 to full output and indicates the output power provided to the trailer brakes, relative to the gain setting.

After the electrical connection is made to a trailer equipped with electric brakes or electric over hydraulic brakes, the TRAILER CONNECTED message will be displayed momentarily on the DIC. The Trailer Brake Display Page can be selected on the DIC showing TRAILER GAIN and OUTPUT, after all vehicle related service messages are acknowledged by the driver. Depending on which instrument panel cluster is in the vehicle, the DIC may display dashed lines, a greyed out display, or it may be blank signifying a disconnected trailer or a trailer brake fault condition.

marpel · July 11

asilverblazer,

Thanks for the detailed attachment (not sure if it actually confused me more or not).

My (layperson's) takeaway is the driver has the most control of the system due to the necessity for setting the Gain and applying brake pedal pressure. Without that (ie Gain left at 0), the truck has no "guidance". In other words, it cannot send current (amps?) to the brakes, assess whether that current is sufficient and, if not, regulate that current.

It just sends what the Controller tells it, based on the Gain setting, and the degree of brake pedal pressure. Less brake pressure, less amount of amps, more brake pressure, more amps sent, to the max of the Gain set by the driver. I think it is a more simplistic system than some give it credit.

However, I may be way wrong on this.

bruceb58 · July 11

16 hours ago, marpel said:

asilverblazer,

Thanks for the detailed attachment (not sure if it actually confused me more or not).

My (layperson's) takeaway is the driver has the most control of the system due to the necessity for setting the Gain and applying brake pedal pressure. Without that (ie Gain left at 0), the truck has no "guidance". In other words, it cannot send current (amps?) to the brakes, assess whether that current is sufficient and, if not, regulate that current.

It just sends what the Controller tells it, based on the Gain setting, and the degree of brake pedal pressure. Less brake pressure, less amount of amps, more brake pressure, more amps sent, to the max of the Gain set by the driver. I think it is a more simplistic system than some give it credit.

However, I may be way wrong on this.

Been reading through your posts. A test I think you should do is to put a current clamp meter around each brake wire going into each drum brake assembly and measure the current at various gain settings when manually applied the brakes with the manual lever. Make sure you only use one of the wires...doesn't matter which one as long as you just put it around one.

Make sure you use a clamp meter that can measure DC current.

BTW...when I first bought my trailer, my brakes basically didn't work at any setting. What I had to do was burnish the brakes. That meant driving at around 40MPH and applying brakes hard to get down to 20MPH. Do this 10 to 20 times letting brakes cool down a little between applications.

Edited July 11 by bruceb58

asilverblazer · July 11

20 hours ago, marpel said:

My (layperson's) takeaway is the driver has the most control of the system due to the necessity for setting the Gain and applying brake pedal pressure. Without that (ie Gain left at 0), the truck has no "guidance". In other words, it cannot send current (amps?) to the brakes, assess whether that current is sufficient and, if not, regulate that current.

Above it says setting the gain to 0 effectively turns off the trailer brakes output.

I would agree that setting the gain is similar to setting guidance for the system in determining a baseline output amount.

20 hours ago, marpel said:

...It just sends what the Controller tells it, based on the Gain setting, and the degree of brake pedal pressure. Less brake pressure, less amount of amps, more brake pressure, more amps sent, to the max of the Gain set by the driver. I think it is a more simplistic system than some give it credit.

It COULD be that simple, I'm inclined to believe it has more programming to it than that.

Chadw90 · July 12

Wow, I missed a lot of good feedback.
BUT just as this mechanic with a heavy electrical background suspected, it was the simple controller/switch (we will call it gain control for simplicity). Swapped it out for the $67 it was and just like that, magically have brakes.
As my original thought right from the start had it, the gain controller was NFG from new. Numbers increased and decreased like it should, but not enough output from it. Its like it had 0,0,0,0,0,0,0,1,2,3 gain settings.
Either way, I sure do appreciate all of you taking the time out of your busy day to dig into this and help. Tons of good information on this thread down different avenues, that Im sure it is going to help many people with similar issues but needing different results.
If it werent for forums like this and people like you, we’d be handcuffed to the competency of our local dealers and unfortunately some of us would not be as fortunate as others.

again, thanks everyone!

marpel · July 12

bruceb58,

Agreed about the clamp meter. This may be the impetus for me to go out and get one.

silverblazer,

Thanks for the continued input. The problem with your belief about the "simplicity" of the system is, I have been unable to find anyone at the dealership with credentials (from techs all the way up to the service manager) who can actually tell me conclusively what does what and how. So if they don't know, how are us commoners supposed to know?.....

marpel · July 12

Chadw90,

You and I were typing and posting at exactly the same time, so I only read your last immediately after I submitted mine.

So, just to be clear, you are talking about the manual brake controller on the dash, not the device recently mentioned that's located under the truck near the spare tire?? As soon as I know for sure, I will go out and get one, on my dime.

Thanks,

Marv