Trailer Brake Issue

[Chadw90]

Yep, the manual one on the dash. It appeared to be working, no reason the believe it didnt other than process if elimination. Dealer changed the 7pin plug. I replaced the whole brake system and if it would signal out to the module in the back on gain 10 and using manually, then the module was receiving signal. So for under $75, it was worth a shot. 

[bruceb58]

5 hours ago, marpel said:

bruceb58,

 

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

 

I have the Fluke 325. It's expensive but a great meter.

 

I am sure there other ones also that will suffice for something like this.

Edited July 12 by bruceb58

[marpel]

Chadw90,

 

I called the Dealer Parts dept about whether they had a brake controller, and price, for my truck. After an incredibly long time on hold, he came back and indicated they had a few in stock and they were $382 (taxes and installation not included).

 

When I questioned this price, he advised me that because the truck had an aftermarket brake controller system, I would need to buy the controller, full harness and control module, as the controller alone would not work with the a/m components.

 

I advised him that I had the OEM controller/system from the factory (up to the point he told me I had an aftermarket, no-one had discussed this at all) and questioned the validity of the unavailability of just the controller. He again put me on hold and finally advised that they had just the controller and the price was $67.

 

I have a service appointment this Friday (tailgate switch recall), but it seems every time I deal with this group, I am getting less confident in their abilities (long story). I am wondering if I can purchase the controller and install it myself, rather than have them do it on Friday.

 

So, can you advise if you replaced the controller yourself and, if so, give me an idea if it is an easy DIY project?

 

Thanks,

 

Marv

[asilverblazer]

On 7/11/2024 at 7:53 PM, marpel said:

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?.....

I doubt they know much more than published information I posted, I'd be interested to do an actual diagnostic of Chadw90's condition to see what tests point to replacing the switch to get better performance. Then compare those same test results to your truck. 

 

In his case there was an actual problem (apparently) and would like to see if that is the same in your case.

 

In any case, all we are 'supposed' to know is what ever the manual says.

[asilverblazer]

11 hours ago, marpel said:

So, can you advise if you replaced the controller yourself and, if so, give me an idea if it is an easy DIY project?

Should be real easy, pull the panel off, unplug the switch, pull it off the panel. Reverse for installation.

[asilverblazer]

Quote

Testing The Truck's Trailer Brake System 

In many cases, trailer brake issues are the result of trailer wiring concerns and they are not related to the actual vehicle's wiring.  Most trailers with these wiring issues do not have high standards in relation to wiring/connections/splices/routing practices (see examples in Step 3 below) when compared to similar automotive practices for wiring/connections/splices/routing.  Because of this, the CCM/BSCM can set faults, which can be hard to determine if they are related to the truck or trailer.  The easiest and fastest way to test the truck is to make a tester using trailer brake magnets.  This type of tester utilizes actual trailer brake magnets and will load the truck's electrical system, just like a trailer would do without having to have the complete trailer.  Shown below is an examples of such a tester.  The trailer brake system will operate with 1 to 4 pairs of trailer brake magnets (1 pair of magnets = 1 axle).  It is suggested to make a tester where the pairs of magnets can be added or removed to equal the same number of brakes as the customer's trailer.  Also, it is advised to make the harness long enough so it can be plugged into the truck's 7 way connector and have the magnets placed into the bed of the truck.  When the tester is connected to the truck, the DIC will display "Trailer Connected" and GDS2 will show "Electro-magnetic" brakes in the CCM/BSCM data parameter "Trailer Brake Type", refer to item 1 in "GDS2 Data" section below .  If so, the vehicle can be driven to see if any fault messages or DTCs set.  If none occur with the tester installed, the truck is operating correctly and the focus should be on the trailer wiring or 7 way connector.  

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Making the Tester

1.  7 way RV trailer connector (example: Pollak Heavy Duty 7-Way Part # 12-706) Qty: 1

2.  Electric Trailer Brake Magnets (example: Dexter Axle Part # K71-104-00)  Qty: 2, 4, 6, or 8

3.  12 gauge wire and terminals/connectors Qty: as needed

Connect two 12 gauge wires to the 7-way RV trailer connector: one to the "Ground" terminal and a second to the "Brake Controller Output" terminal (circuit 47), shown below.  Connect the other ends of the 12 gauge wires to the trailer brake magnets.  All magnets must be connected in parallel so each magnet wire is connected to the Ground and Brake Controller Output wires from the 7 way connector.

Note: Do NOT connect the magnets in series with each other.  

 

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In addition to the tester shown above, GM has recently released a new trailer simulator tool, P/N EL-52641, shown below. When this tester is connected to the truck, the DIC will display "Trailer Connected" and GDS2 will show "Electro-Hydraulic" brakes in the CCM/BSCM data parameter "Trailer Brake Type". If so, the vehicle can be driven to see if any fault messages or DTCs set. If none occur with the tester installed, the truck is operating correctly and the focus should be on the trailer wiring or 7 way connector.

 

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If, after using either of the two tester shown above and the truck functions properly, you may follow the diagnostic tips listed below to help diagnose a trailer related issue.  Trailer issues are NOT covered under warranty, but this information listed below can be used to help the customer/trailer supplier understand and correct any trailer related issues if they so choose.

DIC Message/ DTCs 

It is important to understand and determine what message is being displayed, as well as, if DTC C1114 is setting.  This will help determine what type of fault to inspect for on the trailer.  Below is the combinations of message(s)/DTC to determine the type of fault the customer is experiencing:  

• Check Trailer Wiring message with no DTC.  This symptom is caused after the system detects a trailer and an open and/or high resistance occurs in circuit 47/trailer brake output circuit, during the same ignition cycle. 

  Note: It is normal for the DIC to display "Check Trailer Wiring" when the trailer is disconnected from the truck while the ignition is in the run position.

• Check Trailer Wiring message with DTC C1114 (NO Service Trailer Brake message).  This symptom is caused by a short to ground on circuit 47.
• Service Trailer Brake System with DTC C1114.  This symptom is caused by a short to power on circuit 47 or a poor trailer ground.  

GDS2 Data

GDS2 (scan tool) can be used to view several different data parameters in the CCM/BSCM for the trailer brake system.  The Trailer Brake Type and Trailer Brake Control Output Circuit parameters listed below can be helpful to make sure the CCM/BSCM is detecting the correct trailer brake system in addition to which type of fault it has detected.   

To view "Trailer Brake Type" build GDS2 as follows: CCM/BSCM->Data Display -> parameter "Trailer Brake Type":  "Electro-magnetic",  "Electro-over hydraulic brakes", or "Undefined" (this is displayed with no trailer connected). Example, shown below is a trailer equipped with electromagnetic trailer brakes. 

 

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To view "Trailer Brake Control Output Circuit"  47 faults, build GDS2 as follows: CCM/BSCM->Data Display -> parameter "Trailer Brake Control Output Circuit": Okay, Short to Ground, Short to Power, or Unknown.  Example, shown below is a trailer with a short to ground on the trailer brake circuit.

 

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1.  Trailer Brake Type Parameter

When the trailer is connected, this parameter should be used to make sure the CCM/BSCM has detected the correct type of trailer brakes.  If the CCM/BSCM is detecting the wrong type of trailer brakes, here are several examples that could cause this:

• Refer to the "Trailer Issues" section below items 4 and/or 5.
• A trailer equipped with electromagnetic brakes on only one axle (meaning there is only one pair of magnets) could have a fault with one of the two magnets causing the CCM/BSCM to detect the wrong trailer brake type.   

2.  Trailer Brake Control Output Circuit Parameter

When the trailer is connected, this parameter can be used to help determine what type of fault the system has detected on circuit 47, which could lie within the truck or trailer.

Sample Wiring Diagram

Below is an example of the truck's trailer brake system with the two main circuits that interface with the trailer brake system circled.

Note: As always, use SI to look up the latest wiring diagrams for the vehicle being worked on.

 

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Trailer Issues

1.  The most likely reason for many of these issues is a poor/loose connection between the truck and trailer 7-way connector.

-  It is recommended to use a "Pollak HD" RV trailer connector, as shown in the latest version of PIT5311.  Pollak is the OEM manufacturer of the truck's 7-way connector.  By using a Pollak trailer connector, this will provide the best connection possible.

- For Model Year 2014 to 2018 ONLY -Engineering has released an updated truck-side trailer connector that incorporates a stronger door/cover spring.  This helps to ensure a secure connection between the trailer connector and the truck connector.  If the trailer connector is not being retained securely, replace the truck-side trailer connector with the updated GM part number 23404450, which has the stronger door/cover spring.

2.  Shown below is an example of a 5th wheel trailer where the trailer harness has been routed over the top of the tailgate and plugged into the truck's bumper connector.   While driving down the road, the trailer's wiring harness will bounce up and down (A), causing the trailer's 7-way connector to lose connection (B) with the truck.  The fix in this case was to add the 5th wheel/camper wiring harness and route the 7-way connector's harness inside the box of the truck, as shown (C).  

Note: This same concern can also happen with bumper pull trailers if there is an excessive length of harness.  Securing the excessive trailer harness and installing the Pollak HD RV trailer connector per PIT5311 will help.

 

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3.  Poor trailer wiring connections, as shown below.  General Motors does not recommend these type of connections, but many trailers utilize these connections.  These type of connections are not robust and are not recommended, especially for brake wiring.

 

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4.  Trailer electronic sway control devices. Some trailers may be equipped with electronic sway control devices, like the example shown below. These devices can apply the trailer’s brakes to control trailer sway.   These trailer mounted devices could potentially interfere with the functionality of the factory trailer brake controller resulting in reduced trailer brake performance, or even loss of trailer brakes. Depending on the brand of the sway control device, the following behaviors might be observed:

In some cases, when the trailer mounted sway module activates, it could cause the vehicle to set DTC C1114, and display the “Service Trailer Brake System” message on the DIC. This could be an indication that the trailer brakes are no longer functioning.

In other cases, when the trailer mounted sway module activates, the vehicle could display the “trailer disconnected” message, indicating that trailer brakes are no longer available. Then, when the sway module ceases to activate, the “trailer detected” message might be displayed which could indicate that the trailer brakes were available again.

Some trailer mounted sway control devices could also affect the vehicle’s ability to correctly differentiate between electric or electric/hydraulic trailer brakes.

Before towing a trailer equipped with an electronic sway control device, the customer should contact the device's manufacturer to be sure it is compatible with the GM vehicle.  

Note: If a trailer sways this is likely caused by improper loading of the trailer, refer to the owners manual for more information.

 

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[asilverblazer]

Quote

Conditions for Setting the DTC

C111B 03

The trailer brake power control module detects a voltage below a calibrated threshold on the battery positive voltage circuit.

C111B 07

The trailer brake power control module detects a voltage above a calibrated threshold on the battery positive voltage circuit.

C111B 5A

The trailer brake power control module monitors the battery positive voltage circuit.

C1595 00

The trailer brake power control module detects a short to ground, open or a short to voltage on the trailer brake control signal circuit.

C1596 01

The trailer brake power control module detects a short to voltage in the trailer brake enable signal circuit.

C1596 02

The trailer brake power control module detects a short to ground or an open in the trailer brake enable signal circuit.

C1114 00

The trailer brake power control module detects a short to ground, open, a short to voltage or a plausibility failure on the trailer brake output circuit.

For symptom byte information, refer to Symptom Byte List

Action Taken When the DTC Sets

C111B 03, C111B 07, C111B 5A

• The trailer brakes will be disabled as long as the fault is present.
• The driver information center (DIC) will display a Service Trailer Brake System message as long as the fault is present.

C1114 00, C1595 00, C1595 01, C1595 02, C1596 01, C1596 02

• The trailer brakes will be disabled for the remainder of the ignition cycle.
• The DIC will display a Service Trailer Brake System message for the remainder of the ignition cycle.

Condition for Clearing the DTC

• The conditions for setting the DTC are no longer present.
• The trailer brake power control module clears the history DTC when a current DTC is not detected in 40 consecutive drive cycles.

Diagnostic Aids

• The procedures used in this document are written to diagnose a concern with the customer’s vehicle with no trailer connected. A concern with the customer’s trailer may be the actual cause for a DTC setting or a circuit fault.
• Some customers may experience an intermittent “Check Trailer Wiring” message and/or a “Service Trailer Brake” message with DTC C1114. These concerns may be caused by a poor connection at the 7–way trailer connector. There are several manufacturers of 7–way (trailer side) connectors and many do not comply with the Society of Automotive Engineers (SAE) standard specifications. Some 7–way (trailer side) connector plugs may not properly engage the truck’s 7–way connector socket and cause open circuits. Also, they may cause deformation and excessive wear of the terminals on the truck’s 7–way connector socket. Over time, this will lead to poor terminal tension between the 7–way (trailer side) connector plug and the truck’s 7–way connector socket. Since the trailer brake control module is always monitoring the vehicle and trailer circuits/components, a poor connection at the 7–way connector may cause a “Check Trailer Wiring” message on the driver information center.
• Engineering has recommended the use of Pollak Heavy Duty 7–way (trailer side) connector plugs. Pollak is the Original Equipment Manufacturer (OEM) of the truck’s 7–way connector socket. The use of a Pollak Heavy Duty 7–way (trailer side) connector plug will ensure proper fit when the two connectors are mated.
• If the truck’s 7–way connector socket terminals are deformed or have excessive wear, it will be necessary to replace the truck side connector (use Genuine GM Parts) along with the trailer’s 7–way connector plug using Pollak HD connector plugs.
• Refer to PIT5311 for additional information.

Reference Information

Schematic Reference

Trailer Brake Control Schematics

Connector End View Reference

 

Master Electrical Component List

Description and Operation

 

Trailer Brake Controls Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference

 

Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON.
2. Verify that DTCs U1505, U1556, U2504, P2534, P2535, or any other communication DTCs are not set.
   • If any of these DTCs are set
     Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
    
   • If none of these DTCs are set
   
   
3. Verify the Service Trailer Brake System message is not displayed in the driver information center
   • If the Service Trailer Brake System message is displayed and the customer’s trailer is connected to the vehicle
    
   1. Disconnect the customer’s trailer.
   2. Verify the Service Trailer Brake System message is not displayed in the driver information center.
      • If the Service Trailer Brake System message is not displayed after disconnecting the customer’s trailer, the circuit fault causing the DTC to set is located in the customer’s trailer wiring harness. This is not diagnosed in service information, nor is it covered by GM warranty.
       
      • If the Service Trailer Brake System message is displayed after disconnecting the customer’s trailer
      
      
   3. Refer to Circuit/System Testing.
    
   • If the Service Trailer Brake System message is displayed and the customer’s trailer is not connected to the vehicle
     Refer to Circuit/System Testing.
    
   • If the Service Trailer Brake System message is not displayed and the customer’s trailer is available
   
   
4. Verify the customer’s trailer connection is recognized with a Trailer Connected message in the driver information center.
   • If the Trailer Connected message is not displayed when the customer’s trailer is connected to the vehicle
     Refer to Circuit/System Testing.
    
   • If the Trailer Connected message is displayed when the customer’s trailer is connected to the vehicle
   
   
5. All OK.

Circuit/System Testing

Note:

• You must perform the Circuit/System Verification before proceeding with the Circuit/System Testing.
• The following diagnostic procedure is for factory installed components and wiring on the customer’s vehicle. It will not diagnose a concern with the components and wiring on the customer’s trailer.
• The following diagnostic procedure is based on not having a trailer connected to the vehicle.
• Refer to PIT5311 for additional information before using this diagnostic procedure.

1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the K133 Trailer Brake Power Control Module. It may take up to 2 min for all vehicle systems to power down.
2. Test for less than 10 Ω between the ground circuit terminal 9 and ground.
   • If 10 Ω or greater
    
   1. Ignition OFF.
   2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
      
      
      
   3.  
    
   • If less than 10 Ω
   
   
3. Ignition ON.
4. Verify a test lamp illuminates between the B+ circuit terminal 1 and ground.
   • If the test lamp does not illuminate and the circuit fuse is good.
    
   1. Ignition OFF, remove the test lamp.
   2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
      
      
      
   3.  
    
   • If the test lamp does not illuminate and the circuit fuse is open
    
   1. Ignition OFF, remove the test lamp.
   2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K133 Trailer Brake Power Control Module.
      
      
      
   3.  
    
   • If the test lamp illuminates
   
   
5. Ignition OFF, disconnect the harness connectors at the K38A Chassis Control Module-Auxiliary and S76 Trailer Brake Control Switch, ignition ON.
6. Test for less than 1 V between the signal circuit terminals listed below and ground:
   • K133 Trailer Brake Power Control Module signal circuit terminal 2
   • K133 Trailer Brake Power Control Module signal circuit terminal 5
   • K133 Trailer Brake Power Control Module signal circuit terminal 8
   • K133 Trailer Brake Power Control Module signal circuit terminal 12
   • K133 Trailer Brake Power Control Module signal circuit terminal 14 (if equipped with this wire)
    
   • If 1 V or greater
     Repair the short to voltage on the circuit.
    
   • If less than 1 V
   
   
7. Ignition OFF.
8. Test for infinite resistance between the signal circuit terminals listed below and ground:
   • K133 Trailer Brake Power Control Module signal circuit terminal 2
   • K133 Trailer Brake Power Control Module signal circuit terminal 5
   • K133 Trailer Brake Power Control Module signal circuit terminal 8
   • K133 Trailer Brake Power Control Module signal circuit terminal 12
   • K133 Trailer Brake Power Control Module signal circuit terminal 14 (if equipped with this wire)
    
   • If less than infinite resistance
     Repair the short to ground on the circuit.
    
   • If infinite resistance
   
   
9. Test for less than 2 Ω between the signal circuit terminals listed below:
   • K133 Trailer Brake Power Control Module signal circuit terminal 2 and the K38A Chassis Control Module-Auxiliary signal circuit terminal 23
   • K133 Trailer Brake Power Control Module signal circuit terminal 5 and the K38A Chassis Control Module-Auxiliary signal circuit terminal 22
   • K133 Trailer Brake Power Control Module signal circuit terminal 12 and the K38A Chassis Control Module-Auxiliary signal circuit terminal 30
   • K133 Trailer Brake Power Control Module signal circuit terminal 14 and the K38A Chassis Control Module-Auxiliary signal circuit terminal 17 (if equipped with this wire)
    
   • If 2 Ω or greater
     Repair the open/high resistance in the circuit.
    
   • If less than 2 Ω
   
   
10. Test for less than 2 Ω between the K133 Trailer Brake Power Control Module signal circuit terminal 8 and the Electric Brakes terminal in the trailer brake harness connector in the rear bumper. Refer to the diagram on the trailer brake harness connector cover for the terminal location.
    • If 2 Ω or greater
      Repair the open/high resistance in the circuit.
     
    • If less than 2 Ω
    
    
11. Test or replace the K133 Trailer Brake Power Control Module.
12. Verify the DTC does not set while operating the vehicle within the Conditions for Running the DTC.
    • If the DTC sets
      Replace the K38A Chassis Control Module-Auxiliary.
     
    • If the DTC does not set
    
    
13. All OK.

 

[asilverblazer]

Above is the only other reading I found on the topic... Nothing I read seems to follow a path that results in replacing the switch.

[Chadw90]

Update:

Put a 9000lb load on a 2500lb trailer and hit the road. All way good for the first few brake applications and then all of a sudden no brakes again. Exact same issue as before. It was working fine for the last few trips. Something is either failing that switch or have a major coincidence that after replacing it that it worked for the next 1000kms pulling just fine. 
Mechanic told me that it might just be the intelligence of the truck that it dials the braking back. 
Yes, GM has it programmed to turn the braking effort right down while towing. I just rolled my eyes. 
I said today that I cant drive this truck being it is unsafe to tow with. 
I left it with the trailer and load at the dealership today. 

Edited July 19 by Chadw90

[rjgvt]

I got a call from the dealer today asking if I still have the 2024 GMC that I bought there. I replied yes and he told me that there is a recall for the trailer brake control module. Since I still have the truck, he was going to order the part and let me know when it arrives. 

 

I ordered the truck at their dealership in Oct 23 and picked it up after prep Jan 18, 2024. I just had it their service department this past Monday, July 15, for the second oil change and first tire rotation. Maybe some people trade or sell their trucks with 6700 miles on them!! 

 

I just checked the myGMC app for recalls and the Intermittent Loss of Trailer Brakes recall is on there. Release date: 7/16/2024, the day after I was there. I'm happy they informed me of the recall. I only tow a boat with surge brakes and a utility trailer with no brakes. Ya never know if someone wants me to tow something with electric brakes. 

[marpel]

rjgvt,

 

Coincidently, I was in the dealers today getting the tailgate switch recall taken care of, and purchased a Brake Controller switch for my issue, while I was there. Can you advise if the recall you spoke of is for the '24s only and/or what site I can visit to view the recall notice you speak of?

 

Marv

 

 

[1fast ss]

I just got the recall alert as well. Looks like 2023 and 2024 years are affected. I have attached a pic of the recall. Hope this helps.

Edited July 20 by 1fast ss
Updated information

[rjgvt]

1 hour ago, marpel said:

rjgvt,

 

Coincidently, I was in the dealers today getting the tailgate switch recall taken care of, and purchased a Brake Controller switch for my issue, while I was there. Can you advise if the recall you spoke of is for the '24s only and/or what site I can visit to view the recall notice you speak of?

 

Marv

 

 

My recall is the same as Mickey’s.

[marpel]

1fast ss and rjgvt,

 

Thanks for the response.

 

Weird that the recall only refers to specific intermittent truck years and not ie 20-24. And, also weird that when setting up the Gain (with a just-topped up trailer battery) there was no braking even at Gain 10, and prior to the last trip of last year (again fully topped up trailer battery), again no brakes, however after a number of days during that trip, I noticed a slight improvement in the braking (perhaps trailer battery not as fully charged?). These were when applying the truck brake pedal, but I could get better brake action if using the manual application to the controller.

 

I had a fleeting thought of showing the service rep this recall notice, but as I was recently told when I had exact same squealing brakes that is subject of a GM Recall (same make/model/year) "If you are not on the GM Recall Notice list, we ain't talking to you" (my paraphrase). So, it will be useless for this issue as well, I expect.

 

Marv

[MG386]

I was having the "trailer brakes disabled service required" messages along with check various lights not working message even though the lights were actually working just fine.  Just had my Brake control module replaced this am at the dealer.  they found several trailer codes, hopefully this fixes the issues.  I have EOH brakes on a boat trailer.  no solar chargers,  just the battery for emergency breakaway brakes.

 

CHECK TRAILER BRAKE 2210300 1.30 SCANNED COMPUTER AND FOUND CODES C1114, B1B56, B1B57 AND B1B83. INSTALLED TRAILER BRAKE TESTING MODULE AND FOUND B1883 RETURNED. GAINED ACCESS TO TRAILER BRAKE CONTROL MODULE AND DRAG TESTED MODULE. FOUND PINS DRAG TEST ок. REPLACED MODULE AND CLEARED CODES. TESTED WITH TRAILER BRAKE MODULE AND OK AT THIS TIME.

 

1 85073615 (S) MODULE