JGromada Posted November 24, 2009 Share Posted November 24, 2009 I want to get an order in tonight so a quick answer would be a great help. I have a 98 OBW with auto transmission. I ordered a oxygen sensor (goes into catalytic converter) the one i got has 3 pins but on the car once i disconnect it there are 4 pins on the connector to the car. I am told by the parts place i ordered from there are two! the front has 3 and the back has 4 pins. anyone confirm this? I don't know where the front catalytic converter would be? any help? Quote Link to comment Share on other sites More sharing options...
coldfusion21 Posted November 24, 2009 Share Posted November 24, 2009 (edited) the cat is towards the front of the car. It will have an o2 sensor before and after it. They are probably right, i think all OBD2 cars have two o2 sensors. Yup, there is a listing for a front and back. Sounds like you need the other one. But, how did you determine it was the o2 to begin with? Edited November 24, 2009 by coldfusion21 Quote Link to comment Share on other sites More sharing options...
idosubaru Posted November 24, 2009 Share Posted November 24, 2009 Confirm what? Yes there are two sensors, front and rear. You got the wrong sensor. Technically speaking I believe you can "convert" most 3 wire sensors to work with a 4 wires set up, but I've never done it. Quote Link to comment Share on other sites More sharing options...
JGromada Posted November 24, 2009 Author Share Posted November 24, 2009 I determined there was an oxygen sensor from the OBD codes. When i went to replace it this past weekend it seems like it was actually broken !?! (the center section could move if touched!) I got a good deal on a Bosch universal sensor. Quote Link to comment Share on other sites More sharing options...
Allpar Mod Posted November 24, 2009 Share Posted November 24, 2009 It is mostly common for OBD II models to have two sensors. They are called "upstream" and "downstream", before and after the CAT. One problem with replacing a defective one when they trip a code is that it's hard to determine which one is the offending sensor unless there's physical damage. Still, it's a good practice to replace both at the same time. When one goes bad, often the other is soon to follow anyway. I know they aren't cheap, but often there's little choice anyway. One thing I'll always be an advocate of is shoping around online if you can get away with waiting a few days for any parts, especially pricey ones like these. The last time I bought them, I was also replacing a CAT. I saved mucho $$ shopping around online for the parts. I saved around $15 per sensor shopping for them. I saved $30 on two sensors and only paid $98 for a Magnaflow CAT. No, it wasn't a Soob, but it still would apply to these. Quote Link to comment Share on other sites More sharing options...
JGromada Posted November 24, 2009 Author Share Posted November 24, 2009 I still haven't figured out where the upstream (pre-Cat) Oxygen sensor is? Does anyone have a picture or an illustration they could point me to or share? I am clueless on this. I have replaced the downstream one before, but never the upstream one. thanks Quote Link to comment Share on other sites More sharing options...
idosubaru Posted November 24, 2009 Share Posted November 24, 2009 real simple, follow exhaust, it's the only sensor in the exhaust. right close to where the pipes split - at the "Y" Quote Link to comment Share on other sites More sharing options...
JGromada Posted November 24, 2009 Author Share Posted November 24, 2009 real simple, follow exhaust, it's the only sensor in the exhaust. right close to where the pipes split - at the "Y"Excellent thank you. Quote Link to comment Share on other sites More sharing options...
themoneypit Posted November 25, 2009 Share Posted November 25, 2009 i just replaced both of mine last week. the upstream one is in the front of the cat. i had to get at it from up top. i removed the intake housing (2 10mm bolts and 2 hose clamps) and was able to get at it from the back of the engine bay. the downstream one is in the center pipe near the resonator. this one was easy to get to from underneath the car, but was more rusted and tougher to break loose. after replacing both, the car ran so much better. i do however recommend spending the extra 20 bux to buy the exact fit ones. universal ones at advance auto were 69 bux, exact fit were 90. they had the proper plugs on them and were ready to install. the universal ones were the same part number for both, because you have to splice the old plugs onto the new sensors. i figured since these see alot of abuse under the car ie snow, road debris, etc... id rather have a direct plug in, than several splices in wiring under the car. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted November 25, 2009 Share Posted November 25, 2009 particularly with these newer cars having 3 and 4 wire sensors the few extra dollars makes it nice to make sure it's all right. that being said, it's very simple splicing that can be done in your home/garage/wherever so it's very easy and quick if you're comfortable and have the supplies to do that stuff right. Quote Link to comment Share on other sites More sharing options...
JGromada Posted November 26, 2009 Author Share Posted November 26, 2009 Ok was under there this morning. I can't get the D*** special socket on the oxygen sensor because of that heat shield. So i got out my 22mm open end wrench, but couldn't get enough torque on it. I am letting it soak overnight with Liquid Wrench and i will attack tomorrow. (almost time for Thanksgiving) I have a Bosch Universal Oxygen Sensor and i think i feel comfortable with the splicing. (least of my problems) I am keeping the front Oxygen sensor and will do that too if i can get that off easily. (thanks for the tip about removing it) My next concern is about the Y-Pipes (always something). I think i will make that a new thread. Quote Link to comment Share on other sites More sharing options...
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