Trailer brake not working

[Diggity Dog]

I have a 2018 GMC HD Denali with a Duramax. Great truck, except that I continue to have break controller issues. Now I’m out of warranty and it just went for the 4th time. The dealer back home in Canada has been replacing a module aboveboard spare tire. It also went on me while ion Florida and the dealership repaired although I’m not sure how. 

 

Just went today. Not while towing but within 30 minutes of having as carwash. The 30amp fuse under the dash is fine.  How can I tell if its the module Or if it is the relay I hear so much about?

 

[newdude]

System will set codes.

 

Most common failure part is the switch in the dash, followed by the trailer plug then the module on the frame.  Being it happened in a car wash, I'd suspect the trailer plug had water intrusion.    

 

Also, the fuse for trailer brake are in the UBEC (underhood fuse block).  Fuse #1 is the trailer brake fuse.   

[Diggity Dog]

Fuse is good. 
Trial and error or is there a way to determine whether it’s the switch or the module?

 

Is there a relay as well in the system or is that just in the older GMC models? 

[newdude]

On 5/30/2020 at 2:59 PM, Diggity Dog said:

Fuse is good. 
Trial and error or is there a way to determine whether it’s the switch or the module?

 

Is there a relay as well in the system or is that just in the older GMC models? 

 

Relay was in the GMT-900 trucks.  K2 don't use that.

 

To determine, you'd need a volt/ohm meter and some time.  If all the wiring to the switch test correct, and the module test good, that would lead to the bad switch.  Same for the trailer plug, if you unplug the connector to the trailer receptacle and you've got good ground and power for everything, but when you've got the receptacle in and its dead, that would lead to bad receptacle.

 

Quote

 

DTC C1114, C111B, C1595, or C1596

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.
   • 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.
   • 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.
   • 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.

 

 

1.  

[zmnypit]

I had to take a flat head screwdriver and bend each pin inside the connector outward a fuzz. I've done this on two trucks now and its fixed both. I tried the swapping plugs on the trailer, fuses etc and nothing. Bent the tabs out where contact is now made with the trailer harness and all is well. 

[Diggity Dog]

Funny, just got the same advise on the weekend.

Dealer has it now and is changing the harness from front to back.

This is the 4th time its failed.

I’ve had three new modules, three new relays and now this. I remember back and one mechanic had the harness ripped open, which is likely why it is now corroded and needing replacement. 

Thanks for the feedback.