I'm not sure about NNBS specifically, as I have swapped rotors to aftermarket,
but my 05 had some grooves in it after a while, didn't effect stopping or anything. I'm sure it's just dust and shit causing uneven mating surface.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Some owners may comment on a scored appearance of the front brake rotors. This scoring could be caused by the make up of the front brake lining. The brake lining formula has ingredients to clean rust off the rotor braking surface. This cleaning feature of the rotor braking surface may have a side effect of scoring.
This scored appearance is normal as long as no other symptoms are experienced such as pulsation, roughness, noise, and the scoring does not exceed the specification in SI.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
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