[lagoon69]

I just replaced both o2 sensors on my tracker. First I replaced the upstream with a universal, trying to save myself money, and the code still showed up. After talking to a trusted mechanic, he said he hasn't had real good luck with the universal sensor. So instead of saving $100 I ate $70 for a sensor that was usless. I then bought the oem replacement. Then the engine light came on again. it was the downstream. I replaced that one and everything is fine now. I asked my trusted mechanic friend and he said sometimes only one will go, but more commonly if one goes the other isn't too far behind. The upstream sensor was a little cheaper than the downstream, but yes they both cost near $200 each. and if you have to replace your starter, be prepared to spend a pretty penny on that one too..