Gear oil inside the gearbox helps keep the gears well lubricated and cool. Gear oil prevents the heat caused by metal to metal contact and maintains the transmission in your vehicle. The oil helps the gears to shift smoothly and move the vehicle easily. Gear oil in your vehicle must be maintained according to recommendations and standards set by your vehicle's manufacturer to avoid transmission problems.
Raise the front part of your vehicle with a jack and position jack stands under the frame of your car on both sides. Lower the car onto the jack stands.
Crawl underneath the car and locate the gearbox. It should have a shaft popping out of the middle with two plugs on the front. The higher plug on the gearbox is known as the fill plug, and the lower one at the bottom of the gearbox is the drain plug. The majority of these plugs will have a 3/8-inch square hole in the middle or bolt heads.
Release and loosen the top fill plug with a closed-end wrench if accessible then a 3/8-inch ratchet. Stick your finger in the plug's fill hole. If the gearbox oil is below the fill hole level, then it is full. If the oil level is far lower than this level, then more gear oil needs to be added until it runs out of the hole.
Screw the fill plug back in and make sure it is tightened securely. Raise the car with the jack and remove the stands. Lower the vehicle to the ground.