Troubleshooting Brake Controller on 2002 GMC Sierra 2500 HD

Updated 09/27/2024 | Published 07/23/2008

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Question:

The electronic controller in my 2002 GMC HD 2500 truck stopped working. I tested the voltage sent to the controller and no juice goes through when the brake is pushed. I replaced the switch for the tailights. Is there a specific fuse for the brake controller or a relay? I have gone through the fuse box and cannot seem to find it.

asked by: Rob

Expert Reply:

First, use a circuit tester like part # PTW2993 on the black wire exiting the rear of the controller to verify that power is reaching it. If not, there is a 20- or 30-amp fuse in the power distribution box, located under the hood on the driver's side fender, that is most likely blown. Once the fuse is replaced, you will want to inspect the brake output circuit on the trailer connector, tracing it back to the trailer brake magnets to determine what caused the fuse to let go. Skipping this step will probably mean you will keep blowing fuses.

Will the controller actuate the brakes when the manual override switch is activated? If the brakes work with the switch, but not the brake pedal, there is a different fuse involved. Check your owner's manual for the location of the CHMSL fuse, and check and replace if needed.

You can see additional photos at the links provided.

expert reply by: Mike L

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John R.

8/16/2024

What is the purpose of the blue wire with the connector that is coiled with the red power feed for the brake controller? Left fender fuse panel....

Mike L.

9/27/2024

@JohnR The blue wire carries the brake controller output from the controller to the rear of the vehicle, but in your case it terminates in the engine compartment. You'd want to cut that connector off, graft on a length of 10 gauge wire and route it to the rear of the vehicle to the proper pin of the 7-way. I'll link you to an article that explains all this.

Helpful Links

faq-cbc.aspx