If the automatic transmission does not shift properly and the Check Engine Light illuminates, the speed sensors in the transmission may have failed. The sensors are simple and inexpensive to replace.Google+
Car Problem Reports
Hyundai Sonata Transmission Won't Shift/CEL Due to Failed Speed Sensors in Transmission
Hyundai Sonata Problem
Average Mileage: 128,589 mi (42,000 mi - 220,000 mi)
Visitor, 2004 Hyundai Sonata, 42,000 mi
The check engine light stays on and the transmission does not shift properly.
Transmission won't shift gears/CEL on
Visitor, 2006 Hyundai Sonata, 220,000 mi
want change out of 3rd gear want go in reverse service light on.
Visitor, 1999 Hyundai Sonata, 165,000 mi
rough transmission shift
Visitor, 2001 Hyundai Sonata, 125,000 mi
The transmission seems to be stuck in third gear sometime ,the jerks and engine light comes on
Visitor, 2001 Hyundai Sonata, 120,000 mi
it seems that the transmission doesn't shift properly , than all of sudden you will feel it jolt and the engine light come on