2003 Hyundai Elantra Check Engine Light On

Probably replaced a good sensor. This codes could be from a bad sensor, a vacuum leak, or an exhaust leak before the sensor.

If the check engine light is on and/or flashing you should get the engine computer checked for trouble codes to proceed.

most of the time a engine light will set with an Evap leak code if the gass cap is not tight or left off. tighten cap, or replace cap if gasket is cracked or worn.

Did you use a aftermarket O2 sensor or a genuine Hyundai one? If it's an aftermarket one it may be bad or not as good as the OEM one. See here for more details and other potential causes: P0133

Until you verify which codes occured, your guess is as good as mine. Whenever the 'CHECK ENGINE' light comes on, the ECU (Engine Control Unit) sets a Diagnostic Trouble Code (DTC). These codes identify the particular engine management system which caused the light to come on.
You'll need to use/find an OBDII (On-Board Diagnostic) Scanner to retrieve any code which have been stored in the ECU computer. Afterward, we might be able to help you DIAGNOSE and perhaps eventually fix the problem.

The check engine light usually comes on when there is a faulty sensor. or circuit. Sounds like you may have a faulty throttle position sensor. It would be best to have engine codes read to pinpoint exact problem area. Many part stores do this for free.

Check your engine oil and break oil weather it is in below low level or full, if it has in low level get an engine oil for your car module and pour it. otherwise go to authorized Hyundai service centre and check for it.

NO. These models do not have warnings on the transmission failure. There is warnings only when the transmission encounters electrical component failure, overheating(some cars), low fluid. Usually the warning is the O/D flashing light, or a seperate transmission light. Hopefully this helps

1 - Is your check engine ligh ON - If so have the car checked for codes

2 - Do you notice if your car is harder on fuel - elantra's are known for having an 02 sensor stop working and not turning on the check engine light.

I have a 2004 Hyundai sonata I hear a squealing sound and the car looses power when i start to go. The error code is P0301 any help would be great.
Thanks