Replace the shifter cable when your vehicle fails to switch normally from one gear to another. A failure to switch happens when the shifter cable breaks down.
The shifter cable is a two-spot anchored cable that connects the shifter to the shifting engine arm. To replace a dysfunctional shifter cable, get an adjustable wrench and a new shifter cable that suits the model and make of your car. Using the wrench, loosen off the nut that secures the cable sleeve in place, and remove the sleeve from the anchor, moving the shifter as needed to loosen the connection.
Once the cable is detached from the shifter, locate the connection between the cable and the engine's shifting arm. Unscrew the nut that secures the connection with the wrench, and pull out the cable sleeve from the arm. Check the anchor for damages, and replace it as needed.
To install the new cable, connect the cable to the shifter, and fasten the cable sleeve to the shifting arm with the securing nut. Once the new cable is in place, move the cable through the vehicle gears to ascertain that it hits the gears properly, and fix any defects as needed. Test drive the car.