Hyundai Repair: P2251 Code????, 2004 hyundai elantra, hyundai elantra

Question
I have a 2004 Hyundai elantra gls. Its threw a code (p2251). I believe this mean something is worn with the o2 sensor on the manifold. How can I tell whether it is the sensor itself or something else?

Answer
P2251 indicates a problem in the upstream oxygen sensor's signal circuit.  This problem is most frequently in the oxygen sensor itself, but could also be in the wiring or the engine control module (ECM).  

You won't be able to specifically check the ECM for internal problems, but you can check the wiring (with the aid of a schematic, which you can see with a free account at www.hmaservice.com) with an ohmmeter to be sure the wiring isn't broken or shorted to ground.