On my 2003 WRX I got a P0031 code (bloc 1, sensor 1) while traveling at a high rate of speed. I replaced the front O2 sensor, checked the fuse and there are no shorts in the wires. After clearing the code after about a minute on warming up the car codes again. While trying to figure out why I keep coding I have discovered that I used a downstream Oxygen sensor where I should have used a Air/Fuel upstream sensor. Although they are basically the same things, could this be causing my continual errors? I haven't cross checked my ohm readings (3.6 ohm if I remember correctly on my new wrong front sensor) with my rear sensor so they could be different and would that make a difference?
If anyone can offer some insight? I do understand the obvious answer which is that I used the wrong sensor. However they may be essentially the same item. The car has around 100k miles on it. Any insight as to what problem I may have caused initially or if I should cough up the coin and get the correct sensor will be Greatly appreciated!