The computer is seeing a problem with one or more of your sensors. A scanning tool connects to your computer and displays the codes. You can then look up the codes to see what is failing, and hopefully replace the failing part/parts.
okay folks i went to the shop and they mention that it is a downstream sensor, so i went to NAPA and bought the part 84 bucks, now let me ask could someone guide me as to replacing the sensor, wirings?
Sounds like it'd be an O2 sensor. I don't know where it is down stream though. I know that on my '00 XJ there is no 02 sensor after the last cat (the one just prior to the muffler). I think it's located on the downpipe somewhere. I can't quite picture it right now, haven't been under the hood in a while.
My 98 has one O2 sensor on the exhaust pipe just past where it is connected to the exhaust manifold. Then one right after the catalitic converter. So they are both downstream in my way of thinking, one is just further upstream than the other.
Downstream A and Downstream B
Yep, I looked at a picture I took of the new muff and cat, it's between those two. I was remembering wrong.
All OBDII vehicles will have (at least) 2 O2 sensors. One is before the cat, which sends information to the computer about how the engine is running. The second one is after the cat which is only in charge of monitoring the performance of the catalytic converter.
If it is an o2 sensor you are referring to, it's simple to replace...just unplug the clip, unscrew the old one and screw the new one in (Being very careful not to let the tip of the sensor contact anything while you're putting it in). I'd also recommend applying a coat of "Never-Seez" or other anti-seize compound on the threads before putting the sensor in to make it easier should you need to replace it again in the future...
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