Typically, when a car will move in reverse, but not in forward, the transmission is having issues. The reverse clutch in the transmission may have become dislodged.
When the reverse clutch within the transmission freezes up, it prevents the vehicle from going into any gear other than reverse. This can be caused from problem, such as poor maintenance, lack of transmission fluid and overheating. Other things can cause a transmission to become stuck in a gear, including using the incorrect type of fluid or having shift cables that need adjustment. The first step in diagnosing the problem is to check the fluid level. If the fluid is low, car owners should fill it to the proper level.
A less common reason is the vehicle's computer system has defaulted. To determine if this is the problem, users can try resetting it by unplugging the battery connectors for 10 minutes and reattaching them.
If the fluid level is right and resetting the computer system does not fix the problem, owners might need to consult a mechanic as the transmission may have issues that can only be fixed by a professional. Sometimes, simple fixes are possible, but there are instances where the entire transmission needs replaced.