The 2002 Hyundai Sonata's "Check Engine" light comes on when there is a problem with the sensors that control everything from the emissions system to fuel management to engine knock. When "Check Engine" light comes on, you need to diagnose the problem using an onboard diagnostic scan tool. This scan tool can read the onboard diagnostic computer and retrieve the codes necessary for you to fix your Sonata. When you've found the issue, and fixed it, you need to reset the check engine light on your car.
Pull the hood release lever on the left side of the driver's seat. Then, pull up on the safety latch under the center of the hood. Pull the hood up and support it with the hood support.
Loosen the small nut on the negative battery cable clamp (the cable clamp without the red cover) using a socket wrench. The battery is on the left side of the engine bay.
Pull the clamp up off the negative battery terminal.
Wait 15 minutes and reattach the cable clamp. This will erase the trouble codes and shut off the check engine light.
