2001 Hyundai Sonata check engine light dilemma. I have a 2001 Hyundai Sonata 2.4L that is

Answer 1

I would'nt worry to much about the p0300 anymore as you surely fixed the problem, but you will need to erase the code if autozone will do it for you. This can be caused by cheap gas, sticking egr solenoids or valve, carbon deposits on your pistons and valve (from cheap gas deposits). If your car runs fine and light comes on again then try using higher octane fuels of a different brand.

Your P0401 egr insufficiant flow can be fixed by replacing the egr vacuum solenoid and or the control valve. Both of which are located behind and next to the intake manifold. The solenoid has 2 small hoses and a 2 pin connector mounted to the right side of the intake manifold under 2 bigger connector, one of which sais (sensor/angle). The control valve is only attatched to 2 vacuum hoses and it's directly behind the intake manifold.

Dont let all this confuse you, it's pretty simple if you just look for them. When removed them you might break them as they are brittle so be prepared to replace them or leave them alone as they are only meant to function for emissions purposes.