2003 Elantra code P0140

MIL came on last week on my 2003 Elantra. Tightened gas cap....no help. Pulled code today. P0140. "Insufficient activity from oxygen sensor 2 in bank 1 for current operating conditions". Where exactly is this sensor located? Is there a way to check to make sure it is bad and needs replaced as opposed to bad wire or connector? If I need a sensor... after market or OEM part? Is the sensor change out a difficult job? Special tool needed? If anyone can offer advice, I would greatly appreciate direction.

The downstream O2 sensor is toast. It's fairly common for them to go bad, and even recommended to replace after so many miles on many cars. Either that or bad wire connection, which is unlikely. You'll find it on the exhaust pipe after the catalytic converter. Often times they are seized onto the threads, and it's a biotch to get out. You can get universal ones on eBay for $30 that will do the job as good as any, but you have to cut and splice wires.