On the 2.7L V6 and 2.4L 4 Cylinder, a defective exhaust gas recirculation (EGR) switching valve may cause an intermittent rough or unstable idle engine.
Problems for specific Hyundai Sonata years:
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Most reported 2005 Hyundai Sonata problems
Problems with the accelerator pedal position switch may cause the Check Engine Light to illuminate; an improved switch is available to fix this problem.
Parking lights not turning off intermittently or all the time. The common problem is with the cabin fuse box. Complete replacement of the assembly is necessary to fix the problem.
The timing belt can fail prematurely; if it fails while driving, it can cause catastrophic damage to the engine. Be sure that the timing belt is inspected and replaced according to the manufacturer's recommended schedule.
Prior to replacing the automatic transmission fluid (to improve shift quality), make sure that the transmission fluid level is correct. Also, make sure the computer that controls the transmission has the most up-to-date adaptive programming information. When servicing these transmissions be sure to use fluid approved by Hyundai.