One problem related to fuel injector has been reported for the 2006 Hyundai Sonata. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2006 Hyundai Sonata based on all problems reported for the 2006 Sonata.
Smelled a strong fuel smell inside the car; especially when cold starting; this is 3. 3l v6 engine. Took the car to the dealer and they could not find any problem. This was on and before 22 Sep 2009 with about 48,000 miles on the vehicle. Gas smell getting stronger and personal mechanic found right front fuel injector leaking, especially when cold. Also mileage has dropped about 10 mpg during long road trip. Mechanic recommends change of fuel injector o-ring seal(s) on the leaking injector and all others (5 more). I took the vehicle to the dealer for a warranty repair. Still waiting to see if they will repair the vehicle properly. This could be a serious safety/fire issue with raw fuel being sprayed on the hot engine.