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O2 Sensor Questions

chadhargis

Member
Joined
May 25, 2003
Messages
29
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City, State
Nashville, TN
Year, Model & Trim Level
2003 XLT 4x4 V8
As a former owner of a 1994 Explorer, I decided to purchase another one. I bought a 98 Sport with 4.0 pushrod engine and automatic tranny. The truck has 87,000 miles on it, but I drove my last Explorer to 145,000 miles with no problems other than general stuff.

Here's my problem. I am getting a check engine light and thanks to this great site, I found I could go to Autozone and get the code read. I did, and it turns out that I have a failing O2 senson in "Bank 1". The printout Autozone provided me says Bank 1 is nearest to the engine and bank 2 is the downstream O2 sensor in or near the cat converter. I bought a new O2 sensor and an special socket to remove and replace the part with. I crawled up under the truck and noticed there is a O2 sensor in both sets of headers! SO....which one am I supposed to replace? Once I find that out...how the HECK and I supposed to reach the plug for the O2 sensor. Both are burried WAY down in the engine bay and I can't reach them from the top or bottom. Then I discover while one 02 sensor is fairly easy to change (drivers side) the passenger side sensor is up next to the transmission cooler lines and I can't turn even a small ratchet much less get adequate torque to break the rusty old factory sensor loose.

Any suggestions?
 



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I see you guys are stumped too.

Anyone have any clue as to what O2 sensor I need to replace?
 






I just changed my O2 sensor last week and had a hell of a time finding that info so you lucked out.

Bank 1 is the side of the engine that cylinder 1 is on. On a 99, and most likely all others, that's the passenger side.

Most likely, you're not going to get it out when the pipes are cold. Run it for a while and then be very carefull not to burn yourself.
 






I actually just changed both of my 02's. I have a 95 with the v6 ohv so I dont know how much different mine is than yours. With that many miles I would deff. replace both 02's. I didn't use the tool that you have I used a big *ss wrench and found it worked good. I had 1 02 sensor in each part of the "Y" pipe right after the header. The drivers side was easier than the pass side. In order to disconnect the wire I pulled the harness out of whatever was holding it in. It gave enough slack to make it easier to undo the plug. The plug is a real pita to get undone. I took a small pair of needle nose pliers and broke the little clip holding the two connectors. Make sure you put the new o2 sensor in before connecting the harness and make sure you wear a good pair of gloves.

For the pass side I actually had to take off the little plastic piece in the fender well that is held in with the pop thingy's. In other words the piece that pulls right out. I was then able to grab the harness and pull it apart. I then took my wrench and very slowly (no room under there) took of the O2 sensor. After that I put in the new o2 conncected everything back up and was ready to go.
 






big *ss wrench? lol.

when all else fails grab the biggest tool you got and start hammering :|
 






The thing about O2s is, you're supposed to replace them in pairs. The reason for this is because a brand new O2 sensor will send voltage a certain way, and an older O2 with say, 87,000 miles on it will sometimes return a different voltage. This disparity can wreak havoc with your trucks computer, and the computer won't know how to mix the fuel and air properly. So in your case replace both upstream O2s.

If the O2s are too hard to reach, (and I know what you're talking about and fully empathize) you could have a shop do it. Let them burn themselves. There are lots of threads here about changing the O2s and they have nice tips n' tricks about how do reach them etc.
 






Thanks guys! I'll stop by the parts store and pick up another 02 sensor. The drivers side looks like a breeze to change. I'll try going through the wheel well on the passengers side to unhook it.
 






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