Troubleshooting Integrated Trailer Brake Controller In 2019 GMC Sierra Not Applying Trailer Brakes

Question:

The trailer has 1700 miles on it. Has Dexter triple 7000 pound axles with 12 inch brakes self adjusting. The truck is a 2019 GMC 3500hd. Do you know if the factory brake controller will work with a triple axle trailer?

asked by: Jon

Expert Reply:

I would be happy to help, but that is not a good way to test if your brakes are working or not.

I recommend first checking the make sure that your trailer brakes are adjusted correctly, as if you have not adjusted them and have some miles on the trailer the adjustment is probably incorrect. I included a link a help article that goes over how to adjust the brakes.

Next would be checking the brake magnets of with a multimeter like # PT29ZR. You will need to test each brake magnet and see how many ohms you are getting. Magnets it good shape should have between 3.0-3.8 ohms if you have 10" or 12" brake assemblies, or 3.8-4.0 ohms if you have 7" brake assemblies. If your ohms readings are outside of these specs then they are bad and need to be replaced.

If you can tell me the size of the brakes on your trailer I would be happy to recommend the correct replacements.

expert reply by: Samuel C

Jon

9/21/2021

Samuel C.

9/21/2021

While we do not have the exact specifications of the OEM controller on your Sierra I do believe it is compatible with up to 4 braking axles so it should work with your triple axle trailer, though you will want to call GM to confirm this. Typically issues like this are due to trailer wiring and not usually the integrated controller unless you have electric over hydraulic brakes. Since you mentioned that the trailer is pretty low miles and has self adjusting brakes I would first check that the main ground on the tongue of the trailer is securely connected, and that the trailer connector is securely connected into the 7-way connector on your truck. If that wiring looks good and secure then you will still want to check ohms of the brake magnets. Since you have 12" brakes you should see between 3.0-3.8 ohms. Let me know what you find.