The GMC door mirrors are when the driver is backing into a tight space as well as observing cars approaching the vehicle from behind while on the road. This is an example of one component that serves both a function of safety and a function of convenience. Because of the importance in the way the GMC door mirrors are used, having one on both sides is necessary to properly operate the vehicle so passengers and cargo can be transported safely. On many of the larger box trucks, they are also the only mirrors on the vehicle because a rear view mirror will not be able see what is behind the vehicle. The door mirrors on your truck will never just wear out, but they could become broken in a maneuver when they come in contact with a solid object or another vehicle. This will require their immediate replacement on your GMC truck. With the larger extended door mirrors, only the mirror portion of this component can be replaced by removing the hold down and pivot bolt. On a few of the pickup trucks, they now have an option of being equipped with an electrical controlled door mirror. This is a more complicated procedure where the inner door panel has to be removed and the electrical connections have to be disconnected before you replace the mirror. Because there are electrical components to this part, the battery should be disconnected on your GMC truck during it. The mounting bolts for the door mirror have to be removed then the new mirror can be put into place. Remember to also place the spongy or rubber mounting pad in the right position so the finish on your GMC truck will not be damaged. This will also prevent moisture from entering the inner door when it rains.