The transmission jumps out of third gear while you were driving your car.
Car Problem Diagnosis
Transmissions that jump out the 3rd gear is an indication of a problem of faulty shift linkage or excessive input shaft movement. It is very difficult to understand if you are not a mechanic why the faulty shift linkage or excessive input shaft movement can cause the transmission to jump out of 3rd gear because of the complexity of manual transmissions. However, just understand that shift linkage and standard play of shaft input movement is causing the transmission to stay in gear. Therefore if the shift linkage is faulty of if there is an excessive input shaft movement it can cause the transmission to stay out of gear. The problem we indicated is just a possibility that is more likely the cause there are other cause which can be determined by conducting actual inspection on the transmission.
Possible Cause of Transmission Problem
Faulty shift linkage or excessive input shaft movement
All About Auto Advice
If your car is under warranty your car will be covered for any work that is necessary. Otherwise find a reputable auto repair shop specialized in manual transmission. Ask the mechanic to inspect the shift linkage and adjust if necessary, also ask the mechanic to inspect the input shaft movement if within specifications. If after the adjustments, the problem of the transmission that jump out of 3rd gear still occurs then expect a more costly repair.