Two problems related to transmission sensor have been reported for the 2000 Hyundai Sonata. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2000 Hyundai Sonata based on all problems reported for the 2000 Sonata.
Transmission input speed sensor failure, this problem is shockingly all over the internet, the sensor fails and if your on the highway, you suddenly slam down in speed to almost half your previous speed with a loud bang as the transaxle jumps from 4th gear to 2nd gear and the engine redlines. Due to the failed sensor telling the transaxle to downshift improperly. A inexperienced or less capable driver may have been thrown out of control from the sheer force of the impact when the transaxle mis-shifts from 4th to 2nd when the sensor malfunctions.
Car had a recall for the oxygen sensors and was taken care of. However, it has been in the shop 3 other times to have the oxygen sensors replaced and I just had another go out past the warranty period. I have also had the car 'slam' into a lower gear while on the expressway and the check engine light came on. When I take it they say it is a transmission sensor and replace it. This has done it five times!! it is very scary when it does this. The car is on it's fourth battery and it has 80,000 on the odometer. I have had numerous other problems too. Now it just will not start, it is going to an independent shop this time. This car has been one big headache!!!.