98 Mitsubishi Montero Sport P0141 code

Okay, so I just bought this vehicle for my dad (3.0L, 4x4, 175,xxx miles). Needs a few other things before driving it a lot.
I changed the O2 sensor and cleared the codes. After idling it some, and moving it to a different location just a few feet away, the code is back. Now, I'm thinking possible short in the circuit. However, without a Chilton or Haynes manual available for this vehicle, finding wiring diagrams is turning out to be very difficult. Any help finding one would be greatly appreciated!!

I could only find one O2 sensor and it is located just after the two exhaust pipes merge into one. It looked clean on the outside and all around that area. After pulling it out, it was only a bit blackened. Didn't look bad, but I changed it anyhow.

It also had the code P0170. But it's not back as of yet...

Any ideas would be very helpful!
I will update my progress, and conclusion when it comes.

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Toyota RAV4: 2000, 4 cyl, 2.0 L, Auto, AWD, Moonroof, DRL, Upgrades and Mods, with lots more to come. Check it out: http://www.rav4world.com/forums/garage/1029

Im skeptical that it only uses 1 02 sensor on the whole vehicle! U may have changed the wrong sensor or the brand of sensor u installed maybe a cause!

The code reads: "O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)". So though it obviously has two or more O2 sensors, I probably changed the right one though. Being "Sensor 2". The only thing after that particular sensor is the muffler and tail pipe.

As far as brand, I can't imagine even if it is a cheapo, that it would not work from the get go. I suppose weird things do happen.

I'm going to check a few things today, that I know about, to see if it has a short. I hope I'm not able to find anything as I am not very good at electrical current stuff. But what better way to learn?!

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Toyota RAV4: 2000, 4 cyl, 2.0 L, Auto, AWD, Moonroof, DRL, Upgrades and Mods, with lots more to come. Check it out: http://www.rav4world.com/forums/garage/1029

Oh brother!! I found sensor 2 today. Right out in the open too!! So, I had changed the wrong one. The second sensor is closer to the muffler and now it has a new one. If I don't add anything else in the next month or so (when I actually start driving it), then that fixed it.

Note: one person on a Montero Sport forum suggested to test the sensor's ohms. I tested the new one and got 16 ohms. The old good one tested at 16 ohms, and the bad one tested at 0 ohms. Something to consider.

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Toyota RAV4: 2000, 4 cyl, 2.0 L, Auto, AWD, Moonroof, DRL, Upgrades and Mods, with lots more to come. Check it out: http://www.rav4world.com/forums/garage/1029

yeah provided it's open and stays open! a heater that goes open as it heats up is quite common!