Getting the same message "Service Trailer Brake System" as many other, just posting what fixed mine. 2018 GMC Sierra 2500HD 6.6L Denali. If you start with the "easy fix" as many refer to it and replace the Trailer Brake Control Switch Assembly but this doesn't fix it, check the 30A fuse in space 1 of the fuse block under the hood (Pics attached) Hope this helps.
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Eltrip74
Service Trailer Brake System (My Fix)
Getting the same message "Service Trailer Brake System" as many other, just posting what fixed mine. 2018 GMC Sierra 2500HD 6.6L Denali. If you start with the "easy fix" as many refer to it and replace the Trailer Brake Control Switch Assembly but this doesn't fix it, check the 30A fuse in space 1 of the fuse block under the hood (Pics attached) Hope this helps.
![Image]()
![Image]()
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